getmail is intended as a simple, secure, and reliable replacement for fetchmail. It retrieves email (either all messages, or only unread messages) from one or more POP3, SPDS, or IMAP4 servers (with or without SSL) for one or more email accounts, and reliably delivers into qmail-style Maildirs, mboxrd files, or through external MDAs (command deliveries) specified on a per-account basis. getmail also has excellent support for domain (multidrop) mailboxes, including delivering messages to different users or destinations based on the envelope recipient address.
queue_repair can be used to check or correct most corruptions of the queue in qmail (resulting from filesystem damage, etc). Functionality includes automatic, dynamic determination of UIDs and GIDs. Automatic, dynamic determination of use of big-todo. Handles basic tasks like fixing a queue restored from backups, incorrect ownership or permissions of directories and files, missing or extra split subdirectories, unexpected files or other directories, or creating a valid queue from scratch.
elspy is a layer of glue code that enables you to write Python code to scan email messages at SMTP-time with the Exim MTA (mail transport agent). It also includes a small Python library with common mail-scanning tools, including an interface to SpamAssassin and a simple-but-effective virus detector.
asceticsmtp.py is a very minimal "ascetic" SMTP relay-only mail transport agent. It's intended to be used in conjunction with the mutt mail client to provide SMTP mail transport services. It accepts a mail stream on standard input with recipients specified on the command-line, and forwards the message to a given mailhub. SMTP authentication and SSL transport layer security is supported for recent enough Python libraries.
Quotient is multi-protocol (SMTP, POP, IMAP, SIP, HTTP, Q2Q) server that helps with all your online conversations, be they over email, IRC, IM, mailing lists, or voice over IP. It is written in Python on the Twisted framework, and uses Xapian for search and SpamBayes for spam classification.
CAKE (Key Addressed Crypto Encapsulation) is a bunch of Python and C++ for implementing the CAKE protocol. The CAKE protocol is a protocol in which all messages have source and destination addresses that are public keys. This is in the same way that IP packets have a source and destination address that is an IP address.
QUICA is a Web interface to manage various aspects of email administration. Working as a courier-mta frontend, it can make a quick and easy to use email server. Tasks like creating accounts and forwards can be done easily. It manages domains separately, allowing the delegation of each domain to different people. It's a great tool for your customers if you are a service provider, but also works well for a single domain. Quotas for each account are managed, the number of email messages and hard disk space can be controlled accurately. Internationalization is provided (with some languages included) and you can add your own. The interface allows you to delegate the management to non-sysadmins.
Python SRS Library is a Python translation of the Perl reference implementation for SRS (Sender Rewriting Scheme) with easy to install packaging and built-in sendmail integration. SRS is needed when forwarding mail for SMTP authorization schemes that publish which IPs are authorized to send mail from a domain (for example SPF - Sender Policy Framework). It can also detect forged SMTP bounces by signing the return path for outgoing mail.