Sylpheed-claws seems to be a popular mail-client among the Arch community. The project which started out as a bleeding edge branch for sylpheed became a project of it's own and eventually got renamed: The new name is claws-mail. It properly replaces sylpheed-claws in the repos, but it might take a while until the plugins in AUR will catch up.
Sylpheed-claws renamed
2006-12-08 - Tobias Kieslich