A full stop and start of the server solved the problem. As I'm unable to determine what setting I changed to cause this error to begin with, I'm closing the bug.
The bug in the future would be that restart is not equivilent to stop and start. ** Changed in: dovecot (Ubuntu) Assignee: (unassigned) => Russell Smith Status: Unconfirmed => Rejected -- Initial USER command returns -ERR Unkown command https://launchpad.net/bugs/66863 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs