When comparing gnus vs Sylpheed, the Slant community recommends gnus for most people. In the question“What are the best native e-mail clients for Linux?” gnus is ranked 14th while Sylpheed is ranked 16th. The most important reason people chose gnus is:
Yep, really. From Outlook-mode, where Outlook-typical TOFU mails are “repaired”, up to a high-sophisticated scoring and SPAM filtering, footer lines with quotes, rules depending on the recipient, MIME formatting, boxquotes, etc.
Ranked in these QuestionsQuestion Ranking
Pros
Pro Everything is customizable
Yep, really. From Outlook-mode, where Outlook-typical TOFU mails are “repaired”, up to a high-sophisticated scoring and SPAM filtering, footer lines with quotes, rules depending on the recipient, MIME formatting, boxquotes, etc.
Pro It supports IMAP and POP3
… but you can use DavMail to connect to Exchange server via EWS.
Pro Reliable
No issues with stability or stuff going missing.
Pro Comprehensive settings
Pro Very very lightweight
It is simple and very lightweight where claws mail added a lot of bloat like themes and plugins slypheed keeps it simple.
Cons
Con Difficult documentation
Originally a newsgroup reader, so its documentation uses Usenet terminology for everything -- which is confusing.
Con No encrypted mailbox
Likely hasn't been done by anyone since Calypso/Courier back in the 00's.