MarsSeed [1] filed a deletion request for syncmaildir [2]: Broken orphan from 2019. Upstream not developed since 2020, and repo is archived [a]
As per last maintainer's comment, isync is a viable alternative. It is available from extra repo. [a]: https://github.com/gares/syncmaildir/ [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/syncmaildir/
