MailEnable
MailEnable provides an end to end solution for providing secure email and collaboration services. A recent independent survey reports MailEnable as the most popular Windows Mail Server Platform in the world.
Whether you are a hosting company providing email services to thousands of end users or a small business with a single domain, MailEnable provides a solution that will impress your mail users.
MailEnable provides Windows Mail Server software with features comparable to Microsoft Exchange. It provides powerful messaging services like Exchange ActiveSync, IMAP, SMTP, POP3 and collaboration tools such as calendaring (CalDAV), contacts (CardDAV), tasks and notes.
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Mercury Mail Transport System
Mail from the outside world is received by Mercury and placed in the addressee's mailbox, where the user can access it at any later point. Messages sent by local users to the outside world are passed to Mercury, which then takes whatever steps are necessary to deliver them, removing the burden from the user's workstation and allowing him to continue with other work. If you connect using a dialup connection, then only the mail server needs to be able to access that connection. Your workstations do not need their own modems or Internet accounts. The mail server can continue processing mail even when the client workstations are turned off, allowing functions that depend on a continuously available service, such as automatic replies and auto-forwarding.
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Axigen
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.
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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
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