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Maclean IMAP Server Engine

The Maclean IMAP Server Engine is a toolkit designed for developers who need to implement an IMAP server on top of an existing mailstore. Furnished as C++ source code and licensed as an OEM product, it should be easily coupled with any reasonable message-filing system.

Our current product consists of highly optimized code that can be used to build both 32- and 64-bit servers on Windows and Linux platforms. The engine provides a flexible API that should require only a thin glue layer of code to graft the server onto your mailstore.

Maclean IMAP has been on the market for 20 years and is very mature software that has been integrated into products and services used by tens of thousands of people every day.

Standards Supported

The engine supports IMAP4 rev 1 (RFC 3501) in its entirety along with the following extensions: AUTH (RFC 2195), BINARY (RFC 3516), ID (RFC 2971), IDLE (RFC 2177), Login Referrals (RFC 2221), LOGINDISABLED (RFC 2595), NAMESPACE (RFC 2342), UIDPLUS (RFC 2359), UNSELECT (RFC 3691), Conditional STORE (RFC 4551), ESEARCH (RFC 4731), ENABLE (RFC 5161), LANGUAGE (RFC 5255), LIST-STATUS (RFC 5819) and STATUS=SIZE (RFC 8438). It includes support for Plain, CRAM-MD5, DIGEST-MD5, NTLM and OAuth 2.0 authentication. It also has full support for SSL/TLS using the OpenSSL library.


Designed for use with any message-filing system. Messages may be stored in any format. Small memory footprint makes it very suitable for use in appliance products. Ideal (and widely used) for voicemail systems. Great for providing both a means of ingestion and user access to email archives. Includes optional logging and session-transcription systems. Fully implements all basic IMAP4 commands plus many extensions. Extensively customizable. Supports multiple authentication mechanisms.


You can license Maclean IMAP and interface it to your required message store yourself (with the help of our expert technical support of course) or you can contract with us to do it for you. We also offer SMTP code, POP code, even a proprietary mailstore (all at no extra cost) if you need them.

Licensees of Maclean IMAP include one of the largest and best known software companies in the world which has integrated it one of their major products. (We are not at liberty to identify the enterprise concerned.)

As far as we know, the Maclean IMAP Server Engine is the only product of its type. And it’s backed by Pete Maclean whose other protocol engines have been licensed by Apple Computer, Borland, MCI, Microsoft, Verizon and many other well known companies.

Contact us now and learn how we can help you get your IMAP server up and running more quickly than you ever imagined! (Typical time to interface to a new mailstore is less than one month and can be as little as a couple of days.)


Please view our product specifications page or download the document as a PDF file.


You can evaluate the engine by running MIMS, our standalone IMAP Server for Windows (2003/2008/7/8.1/10/2012). MIMS is completely free software that you are welcome to use in any way you find useful.

Download MIMS version 3.50 32-bit.

Download MIMS version 3.50 64-bit.

When the download is complete, unzip the MIMS package to a new directory; no further installation is needed. This package includes executables, a configuration program, and a full HTML-help manual (MIMS.chm).


You can also download our Developer’s Guide PDF. It describes how to use the IMAP Engine.


Our standard license costs US$25,000. This gets you full source code, manuals, samples, royalty-free distribution rights for a single platform (Windows or Linux) and developer support for one year. A restricted-functionality edition tailored for voicemail applications can be licensed for $15,000. Rights to a second platform cost an additional 50% of the original licensing fee.

Want to know more?

Please read our FAQ for Maclean IMAP.

Other platforms

Do you need IMAP server code for another platform (AIX, HP-UX, Mac OS X, Solaris, FreeBSD, OpenVMS)? Please ask us; we have over 20 years of experience porting email client and server code.