Beam (BEware, Another Mailer) is an open source e-mail client for BeOS (R5 and onwards) that aims to be fast, stable and feature-complete.
Beam was created by Oliver Tappe and is copylefted by means of the GPL.
Multiple Mail-Accounts (POP & SMTP), with support for default-acounts and automatic selection of appropriate account when replying, etc...
Fully MIME compliant (Beam passes the MIME-Torture-Test)
Performance adequate for large mail-folders (>10000 msgs), with optional mail-caching
POP-authentication (POP3, APOP, CRAM-MD5, DIGEST-MD5)
SMTP-authentication (SmtpAfterPop, PLAIN, LOGIN, CRAM-MD5, DIGEST-MD5)
Many configuration options, esp. for mail-construction.
Full header-control, you can directly edit mail-headers before sending a message
Stability (I hope - having used Beam for years now as my main email-client with only a few problems)
Filter capabilities (using SIEVE and a SPAM-filter)
Identities, separating the user-info (name, mail-address, signature) from the network-info (server-address, login & password)
Full Support for people-files (you can create, edit and use them)
Secure Transport (TLS, SSL), by means of OpenSSL
Preliminary IMAP-support (fetches mails just as POP3 does)
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