I keep getting the following error in the logs from the imap container:
imap_1 | Jan 03 10:14:03 imap([email protected]): Error: stat(/mail/[email protected]/.dovecot.sieve/tmp) failed: Not a directory

I'm also seeing a "dovecot" dir in my mail client, with a "sieve" subdir, which corresponds with this.

Looks like we've hit this issue:
https://dovecot.org/list/dovecot/2009-October/043593.html

all dot-files/dirs are automatically recognized as mail folders. Possible solutions:

• add maildir_stat_dirs=yes to the dovecot config.
• move existing dot-files out of the maildir