Timo, My first assert in beta2. Syslog said:

Jan 24 09:57:16 emerald dovecot: [ID 107833 mail.error] imap(user): Cached message offset 94625 is invalid for mbox file /var/mail/m/user Jan 24 09:57:16 emerald dovecot: [ID 107833 mail.error] imap(user): file mbox-sync.c: line 1471 (mbox_sync_do): assertion failed: (!sync_ctx->mbox->mbox_sync_dirty || (flags & MBOX_SYNC_UNDIRTY) == 0)

Gdb analysis on the core file is attached. My setup: Solaris 9, mbox format, mbox on NFS filesystem (also S9), index files on local UFS filesystem.

Jeff Earickson Colby College