If the first message in an mbox is deleted by an external program, therefore removing the X-IMAPbase header, an error such as the following occurs.

Apr 9 20:10:51 sm1 dovecot: imap(306812): file mbox-sync-update.c: line 460 (mbox_sync_update_header_from): assertion failed: (ctx->mail.uid == 0 || ctx->mail.uid_broken || ctx->mail.uid == mail->uid)

This prevents the user from logging in, but also appears to cause mbox corruption.

If the X-IMAPbase and the X-UID headers are missing, Dovecot will insert them successfully, but fails to do so when only the X-IMAPbase header is missing.

Using dovecot-1.0.beta3.