When comparing Seamonkey vs Sylpheed, the Slant community recommends Sylpheed for most people. In the question“What are the best e-mail clients for Windows?” Sylpheed is ranked 12th while Seamonkey is ranked 20th. The most important reason people chose Sylpheed is:
No issues with stability or stuff going missing.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Not just an e-mail client
Seamonkey is more than just an e-mail client as it is a full featured web browser as well. This makes for a good app to use for those that dislike having many different apps on their devices as it is a bit like an all in one solution.
Pro Auto imports setting from Thunderbird
For those that would be making the switch from the Thunderbird e-mail client setup is quite easy with Seamonkey as it auto imports all previous Thunderbird settings.
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 Permanent CPU usage
Seamonkey permanently uses CPU (quite a few percents on a Intel i7). On a laptop this causes the fan to run (which make noise) and the battery to lasts less time.
Con No encrypted mailbox
Likely hasn't been done by anyone since Calypso/Courier back in the 00's.