Best Mail Servers for Startups of 2025

XgenPlus

Bharat Sync Technologies Pvt. Ltd.

XgenPlus is a next-generation, feature-rich, and highly secure email solution designed to meet the growing communication needs of businesses, enterprises, and individuals. Developed by Bharat Sync Technologies Pvt. Ltd., Xgen Email stands out as the first email service in the world to support Internationalized Domain Names (IDN), enabling users to create email addresses in multiple Indian languages such as Hindi, Gujarati, Tamil, Telugu, Punjabi, and Urdu. With cutting-edge security features, real-time tracking, advanced collaboration tools, and seamless mobile and desktop integration, Xgen Email ensures that users get the most efficient, private, and productive email experience. Whether you're a startup, a large enterprise, or an individual professional, Xgen Email is the best choice for a secure, smart, and efficient email solution.

1 Rating

Starting Price: Free

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Kerio Connect

Aurea

Secure, enterprise-style email, calendar & collaboration without the high cost. Kerio Connect delivers all the features and functionality for collaboration and messaging solution without the complexity and high price tag of other systems. Email is integrated with shared calendars and scheduling, contacts management, tasks, notes, shared and public folders, and instant messaging. Synchronize messages by direct push to your choice of mobile device via Microsoft ActiveSync. Instant Messaging is XMPP-compatible and can be used from various 3rd party chat/IM applications on desktop and mobile phones. You can install Kerio Connect in 10 minutes and users can be up and running in just 10 minutes more. Kerio Connect can be deployed on-premises or in partner-hosted cloud environments. Deploy for users on Mac, Windows, or Linux; plus full support for Outlook (Windows and Mac) and many other IMAP or POP compliant email clients.

2 Ratings

Starting Price: $36.50

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SmarterMail

SmarterTools

SmarterMail is the ideal Microsoft Exchange alternative. It’s the only business email server on the market that offers native support for Exchange protocols: MAPI, EWS, and EAS, without requiring any additional software or plug-ins for Microsoft Outlook or other desktop or mobile clients. It delivers all the features of Exchange at a fraction of the cost. SmarterMail also includes audio/video group chat and Online Meetings for team collaboration at no extra charge. Its newest feature, the SmarterMail Marketplace, enables seamless integration with platforms like OnlyOffice, Collabora, and AI tools such as OpenAI’s ChatGPT. Available for both Windows and Linux, SmarterMail has lower hardware requirements, superior stability, and reduced maintenance costs. It’s the perfect solution for businesses of any size or industry seeking Exchange-level functionality, without the high costs.

Starting Price: $500.00/one-time

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KumoMTA

Kumo Corp

KumoMTA is an Open-Source, enterprise-grade email message transfer agent (MTA) software for sending high-volume, business-critical emails. KumoMTA is typically chosen by high-volume email users looking to replace PowerMTA, Momentum, or traditional Open Source MTAs. KumoMTA offers high-performance message relay to the tune of millions of messages per hour per server, combined with extreme flexibility and configurability through its use of a Lua scripting engine for configuration and message management. For more information on KumoMTA see our Sourceforge project page.

Starting Price: $0

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Axigen

Axigen Messaging

Offer your customers secure, business-level email hosting with various value added services. An excellent solution for SPs, suitable for thousands to millions of users. Acquire new customers by offering a premium email server solution with a high degree of flexibility, allowing you to automate it within your existing infrastructure. Manage your email, organize and share calendars, sync your mobile devices, all based on a secure and powerful mail server. The perfect answer for businesses of all sizes. Axigen is quite knowledgeable, out of the many hats it wears, take a peek inside and choose what fits you. Manage your email and get stuff done easily with calendars, tasks or notes. Enjoy desktop usability in your browser via keyboard navigation and shortcuts, drag-and-drop, "live" email list view, frequent folders, email filters, out-of-office messages, individual blacklist / whitelist.

Starting Price: $266 per year

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NethServer

Analyzes all web traffic and blocks selected websites via HTTP and even HTTPS using Squid proxy. Integrated with ClamAV antivirus and site blacklists. Multi-domain web server with ready LAMP stack. Virtual hosting allows to host multiple domain names on a single server. Based on NextCloud provides universal access to your files via the web, your computer or your mobile devices, wherever you are. Provide a private Slack-alternative with Mattermost. Open source messaging platform that enables secure team collaboration. Modern and powerful web interface based on Cockpit that simplifies common administration tasks, very easy and fast installation. Based on CentOS/RHEL, a widespread and popular server distribution, trusted by routine security updates, and rock solid stability.

Starting Price: €48 per year

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Zentyal

Join Windows® clients to the domain and manage them transparently. No disruption to your users, no user or device CALs. Comes with industry-standard SMTP and POP3/IMAP mail server built upon the most established technologies and protocols. Guarantees reliable and secure Internet access and helps to manage all the basic network infrastructure services. Receive software updates until the EOL-date of each version and get support when needed. Zentyal offers an easy to use Windows Server® alternative. It comes with native compatibility with Microsoft Active Directory® allowing you to join Windows® clients to the domain and manage them easily, causing no disruption to your users. Zentyal includes the industry-standard SMTP and POP3/IMAP mail servers built upon the most established technologies and protocols. Gives you the opportunity to deploy Zentyal as a mail server, domain & directory server with mail or all-in one server.

Starting Price: €195 per server

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iRedMail

The right way to build your mail server with open source softwares. Works on CentOS Stream, Rocky, Alma, Debian, Ubuntu, FreeBSD, OpenBSD. With iRedMail, you can deploy an OPEN SOURCE, FULLY FLEDGED, FULL-FEATURED mail server in several minutes, for free. We did the heavy lifting of putting all the open source components together and applying best practices. Our product does all the major tasks for you. Furthermore we offer professional support to back you up in case you have some problems. You have all personal data on your own hard disk, you can control the email security, inspect transaction log. No other organization can see the content of all messages. All components used in iRedMail are open source softwares, and you get the bug fixes and updates from the Linux/BSD venders you trust. iRedMail is the right way to build your mail server with open source softwares.

Starting Price: Free

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Mail-in-a-Box

Mail-in-a-Box lets you become your own mail service provider in a few easy steps. It’s sort of like making your own gmail, but one you control from top to bottom. Technically, Mail-in-a-Box turns a fresh cloud computer into a working mail server. But you don’t need to be a technology expert to set it up. Each Mail-in-a-Box provides webmail and an IMAP/SMTP server for use with mobile devices and desktop mail software. It also includes contacts and calendar synchronization. The box also includes other standard mail functionality like spam protection (spam filtering and greylisting), mail filter rules, email client autoconfiguration, and automated backups to Amazon S3 and other services. The box also includes automatic DNS configuration when you let it become your nameserver so that it can set important DNS records for mail deliverability and security including SPF, DKIM, DMARC, and MTA-STS. When enabled, DNSSEC (with DANE TLSA) provides a higher level of protection.

Starting Price: Free

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Modoboa

Regain your independence and protect your privacy by installing your own email server. It takes less than 10 minutes! Create your mail server for free in less than 10 minutes with Modoboa When it comes to create a mailbox, you generally have several solutions: - Use the services offered by Internet providers (Orange, Vodafone...) of infrastructure providers (OVH, Gandi...) with a monthly or annual subscription. However, customization and configuration possibilities, domains and mailboxes number are limited. - Use the services of free email providers (Gmail, Live, Yahoo...) which are limited and your data is used for commercial purposes. - Install your own email server, which requires important technical knowledge to setup and configure the system. Modoboa is an alternative to those 3 options. It frees you from dependence on email providers and makes accessible to all the creation his own secure email server. The whole thing, in less than 10 minutes and freely.

Starting Price: Free

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Mailu

Mailu is a simple yet full-featured mail server as a set of Docker images. It is free software (both as in free beer & as in free speech), open to suggestions and external contributions. The project aims at providing people with an easily setup, easily maintained and full-featured mail server while not shipping proprietary software nor unrelated features often found in popular groupware. Main features include: Standard email server, IMAP and IMAP+, SMTP and Submission with autoconfiguration profiles for clients Advanced email features, aliases, domain aliases, custom routing Web access, multiple Webmails and administration interface User features, aliases, auto-reply, auto-forward, fetched accounts Admin features, global admins, announcements, per-domain delegation, quotas Security, enforced TLS, DANE, MTA-STS, Letsencrypt!, outgoing DKIM, anti-virus scanner, Snuffleupagus, block malicious attachments Antispam, auto-learn, greylisting, DMARC& SPF, anti-spoofing

Starting Price: Free

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Apache James

The Apache Software Foundation

James stands for Java Apache Mail Enterprise Server. It has a modular architecture based on a rich set of modern and efficient components which provides at the end complete, stable, secure, and extendable Mail Servers running on the JVM. Create your own personal solution of email treatment by assembling the components you need thanks to the Inversion of Control mail platform offered and go further customizing filtering and routing rules using James Mailet Container. The Apache James project wires together the different libraries composing James to provide running services, ready to download on the Apache mirrors.

Starting Price: Free

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Horde

Horde is the most flexible groupware on the planet, and that makes it the perfect platform on which to build your business productivity software. Horde connects to (and officially supports) more backends (all the leading SQL, LDAP, IMAP, Sieve, SMTP, cache platforms available today) than any other open source groupware system. This means you can continue to use your existing userbase and your users do not have to remember any additional passwords. Horde's feature set rivals the largest enterprise email systems. We have an incredible feature set that compares favorably against any competition in our primary apps (mail, calendar, address book), and even more in our secondary apps (time tracking, wiki, ticketing, and more).

Starting Price: Free

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Haraka

Haraka can serve thousands of concurrent connections and deliver thousands of messages per second. Haraka and plugins are written in asynchronous JS and are very fast. Haraka has very good spam protection (see plugins) and works well as a filtering MTA. It also works well as an MSA running on port 587 with auth and dkim_sign plugins enabled. Haraka makes no attempt to be a mail store (like an exchange or postfix/exim/qmail), an LDA, or an IMAP server (like Dovecot or courier). Haraka is typically used with such systems. Haraka has a scalable outbound mail delivery engine built in. Mail marked as relaying (such as via an auth plugin) is automatically queued for outbound delivery. Haraka's plugin architecture provides an easily extensible MTA that complements traditional MTAs that excel at managing mail stores but do not have sufficient filtering.

Starting Price: Free

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OpenSMTPD

OpenSMTPD is a free implementation of the server-side SMTP protocol as defined by RFC 5321, with some additional standard extensions. It allows ordinary machines to exchange emails with other systems speaking the SMTP protocol. Started out of dissatisfaction with other implementations, OpenSMTPD is a fairly complete SMTP implementation. OpenSMTPD is primarily developed by Gilles Chehade and Eric Faurot, with contributions from various OpenBSD hackers and members from other communities.

Starting Price: Free

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SOGo

SOGo is a fully supported and trusted groupware server with a focus on scalability and open standards. SOGo is released under the GNU GPL/LGPL v2 and above. SOGo provides a rich AJAX-based Web interface and supports multiple native clients through the use of standard protocols such as CalDAV, CardDAV and GroupDAV, as well as Microsoft ActiveSync. SOGo is the missing component of your infrastructure; it sits in the middle of your servers to offer your users a uniform and complete interface to access their information. It has been deployed in production environments where thousands of users are involved.

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Scalix

Offer a high value Outlook experience with push email, PIM, group calendaring, free/busy services, public folders, delegation, and more. Increase margins with lower server counts and compelling subscription pricing. Reduce your licensing costs and leverage your teams' existing skills with a Linux-based platform. Scalix starter packs are robust, single-server messaging solutions designed to provide smaller businesses and organizations with a full featured email and collaboration solution. Scalix small business edition is our single-server solution designed for small businesses. It includes a rich package of business functionality including a means to instantly recover deleted items on a user-specific basis, wireless device support and more.

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Dovecot

Dovecot is an excellent choice for both small and large installations. Dovecot is among the best performing IMAP servers while still supporting the standard mbox and Maildir formats. The mailboxes are transparently indexed, which gives Dovecot its good performance while still providing full compatibility with existing mailbox handling tools. Dovecot is standards compliant. Dovecot passes all IMAP server standard compliancy tests while most other servers fail many of them. Dovecot’s indexes are self-optimizing. They contain exactly what the user’s client commonly needs, no more and no less. Dovecot is self-healing. It tries to fix most of the problems it notices by itself, such as broken index files. The problems are however logged so the administrator can later try to figure out what caused them. Dovecot tries to be admin-friendly. Common error messages are made as easily understandable as possible.

Starting Price: Free

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Poste.io

analogic

You can have a fully functional mail server installed in a few minutes, mostly waiting for scripts to do the work. The whole package is designed with reasonable defaults to get you up and running quickly, without having to know the internals and without making decisions that could break the email system. User data and configuration is strictly separated from binaries. User database is stored in SQLite database - in file. This makes Poste.io fully compatible with external storage. Migration, backups or updates are therefore very easy and mostly consist of files manipulation. Poste.io has been built from the ground up with security in mind. Internet history is littered with painful security incidents, so we traded old email client compatibility and insecure authentication methods for features that meet today's for features that meet modern security requirements.

Starting Price: Free

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Citadel

Email, collaboration, groupware, and content management - up and running in minutes, on your own hardware, or in the cloud. Citadel is easy, versatile, and powerful, thanks to its exclusive room-based architecture. No other platform seamlessly combines so many different features using this familiar and consistent metaphor. Citadel is 100% open source software using the GNU General Public License. It's not a crippled, cut-down version of some expensive "enterprise" edition. The software you download here is the very best available, and it's all free software.

Starting Price: Free

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IceWarp

The only office rule is, there is no office. Business email, TeamChat for project teamwork, real-time office document collaboration and online meetings. All in our secure cloud and for half the usual cost. Chat in teams organized around projects, upload files, mention coworkers, comment on posted emails, pin important posts. Integration with email enables sharing received messages directly to TeamChat room for colleagues‘ attention. Skyrocket your office work effectivity with Desktop Client and Desktop Office documents on Windows as well as Linux devices. Get the complete Suite, or choose only the app you need.

Starting Price: $312.00/year/user

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Kopano

We provide you with your digitally sovereign solution to keep track of your e-mails and calendars, to organize yourself with tasks or to stay in contact with team colleagues via video meeting. Kopano Groupware is an e-mail and calendaring solution, which can be operated digitally sovereign. Its functionality is comparable to that of Microsoft Outlook and Exchange. Kopano Groupware installations can be operated with more than 100,000 users. Kopano Groupware is an e-mail and calendar server that provides users with their daily communication and organizational data on all devices and connects teams. Data can be jointly edited in public folders or shared with others from your own inbox.

Starting Price: $17 per year

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Exim

Exim is a mail transfer agent (MTA) used in Unixllike operating systems. The first version was written in 1995 by Philip Hazel for use in the University of Cambridge Computing Service's e-mail systems. Exim is distributed under the GPL, and therefore is free to download, use and modify. Exim somewhat resembles Smail 3, but it has diverged and now surpasses it in user friendliness and flexibility. They both follow the Sendmail design model where a single main binary controls all the facilities of the MTA. This monolithic design is considered by some to be inherently less secure and slower, but despite this, Exim's security record is much better than Sendmail and comparable with Qmail and Postfix, as is its speed. In advanced areas such as queue handling, address routing and testing, it exhibits excellent performance. Exim doesn't have a Graphical User Interface (GUI) to help you configure it, but some Linux distributions add one.

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Dovecot Pro

Open-Xchange

Dovecot Pro is a full-service email platform that delivers dynamic scalability, high performance, efficient utilization of hardware, and outstanding support to the world’s largest Telcos, ISP's, and Hosters. With a marketshare of 76% of installed email backends, customers trust the performance of Dovecot Pro. Efficient hardware utilization and advanced monitoring tools for statistics and administration reduce ownership costs and save time and maintenance costs. In addition, Dovecot Pro scales up and out to hundreds of servers and millions of users and multiple physical sites. Its stateless native architecture offers maximum flexibility as each major component can be deployed on its own dedicated node. Dovecot Pro provides industry-leading support for all email standards necessary to provide both Mail Delivery Agent functionality (via LMTP and Sieve), and to facilitate mail retrieval by mail clients (via IMAP and POP3).

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Courier

Double Precision, Inc.

The Courier mail transfer agent (MTA) is an integrated mail/groupware server based on open commodity protocols, such as ESMTP, IMAP, POP3, LDAP, SSL, and HTTP. Courier provides ESMTP, IMAP, POP3, webmail, and mailing list services within a single, consistent, framework. Individual components can be enabled or disabled at will. The Courier mail server now implements basic web-based calendaring and scheduling services integrated in the webmail module. Advanced groupware calendaring services will follow soon. The Courier mail server's source code should compile on most POSIX-based operating systems based on Linux, and BSD-derived kernels. The Courier mail server should also compile on Solaris and AIX, with some help from Sun's or IBM's freeware add-on tools for their respective operating systems. The Courier mail server evolved out of several related projects, that merged together (more on that later). The Courier mail server implements SMTP extensions for mailing list management.

Starting Price: Free

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Cyrus IMAP

The Cyrus Team

Cyrus IMAP is an email, contacts and calendar server. Cyrus is free and open source. Features: Speed Security Efficiency Search CardDAV and CalDAV support Robust data storage Replication Scalable for large installations Flexible filtering support through Sieve Supports antivirus and antispam toolkits Handles deliverability: SPF, DKIM, DMARC Extensive authentication options, through Cyrus SASL JMAP support Long list of supported standards

Starting Price: Free

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qmail

qmail is a secure, reliable, efficient, simple message transfer agent. Security isn't just a goal, but an absolute requirement. Mail delivery is critical for users; it cannot be turned off, so it must be completely secure. qmail's straight-paper-path philosophy guarantees that a message once accepted into the system, will never be lost. qmail also optionally supports maildir, a new, super-reliable user mailbox format. Maildirs, unlike mbox files and mh folders, won't be corrupted if the system crashes during delivery. Even better, not only can a user safely read his mail over NFS, but any number of NFS clients can deliver mail to him at the same time. qmail is vastly smaller than any other Internet MTA. Other MTAs have separate forwarding, aliasing, and mailing list mechanisms. qmail has one simple forwarding mechanism that lets users handle their own mailing lists.

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Oracle Communications Messaging Server

Oracle

Oracle Communications Messaging Server is a standards-based Internet messaging server designed for high-capacity, reliable message handling for service providers and their customers. Messaging Server provides support for several email protocols and can manage embedded text, sound, graphics, video files, and other files and formats.

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ClearOS

ClearCenter

Applications and an operating system come with your computer, tablet, and phone. So, why not on your server? HPE is redefining the small business server by offering ClearOS with HPE ProLiant servers. ClearOS is a simple, open, and affordable operating system with an intuitive graphical web-based user interface and an application marketplace with over 100 apps to choose from, with more being added every day. Leveraging open source software, you decide what applications you need and only pay for the applications and support you want. HPE and ClearCenter are making it easy for small, home, remote, and branch offices to have a server ready to use, out of the box, at no additional cost. HPE ProLiant integrated with ClearOS offers a simple, affordable, and secure experience. Building the IT solution that is just right for you has never been easier.

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Halon

Halon MTA makes you more competitive, by secure and timely delivery of important emails and rapid feature implementation. At the same time, you will cut your development and maintenance costs by half. The Halon MTA is a flexible email operation and security platform. It enables organizations that operate large-scale email services to offer competitive features by rapid implementation and to lower maintenance costs through reliable deployment and reduced complexity. Halon MTA consolidates your email infrastructure, reducing risk and complexity. It makes email infrastructure scalable, simple to manage, rich in functionality and easy to evolve. Suffering from slow and costly implementation of email features and new standards, leading to poor end customer experience? Halon increases email service competitiveness by enabling rapid implementation and reliable deployment. In contrast to traditional layered email infrastructure, Halon's holistic approach cuts system complexity.

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Best Mail Servers for Startups

Compare the Top Mail Servers for Startups as of June 2025

What are Mail Servers for Startups?

XgenPlus

Kerio Connect

SmarterMail

KumoMTA

Axigen

NethServer

Zentyal

iRedMail

Mail-in-a-Box

Modoboa

Mailu

Apache James

Horde

Haraka

OpenSMTPD

SOGo

Scalix

Dovecot

Poste.io

Citadel

IceWarp

Kopano

Exim

Dovecot Pro

Courier

Cyrus IMAP

qmail

Oracle Communications Messaging Server

ClearOS

Halon