[Dovecot] Problems getting Dovecot to work.

Hi, having a nightmare trying to get dovecot working on my SheevaPlug (flash based ARM embedded device). I need to use virtual users, and I need to store all the mail on an external USB HDD (not in home directories which live in the limited flash space). However I can't even log in via telnet. I've followed the Wiki troubleshooting tips, and still no further forward.

logging via telnet, I get: "user sheeva BAD Error in IMAP command received by server." the logs show: ubuntu dovecot: User sheeva is missing UID (see mail_uid setting)

What do I need to do? I know basic Linux stuff, but I wouldn't call myself an expert, so please no tech talks!!!

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