[avar]

Sure, you sync them locally with e.g. offlineimap, and specify a "remotepasseval" key in your config which can invoke a command that invokes whatever password manager you use, same for sending.

I don't do this and just keep my password in plain-text and use full-disk-encryption, because I don't want to have to be constantly unlocking a keyring to have some background E-Mail syncing job work.