Postifx user unknown in local recipient table

Question

Good morning --
My fetchmail job has been failing to get mail to my mailbox with this error (presumably from Postfix):
SMTP error: 450 4.1.1 <username@localhost>: Recipient address rejected: User unknown in local recipient table
(I replaced the actual user name with "username")
I'm not sure what to make of this. "username" definitely exists -- I just su'd into his account and ran the fetchmail job that gave me the error.
The problem goes away if I stop and restart postfix, but it seems to come back pretty consistently (I haven't had a chance to figure out the precise timing).
Any suggesitons?

Answer 1

Thanks, Mihalis.
I do not us su -l -- just plain old su. And echo $USER returns the correct user (that is, the one I su'd into).
I don't think the problem is fetchmail. It's the same result whether I run it from the prompt ("fetchmail -v") or from the user's cron.
The problem resolves temporarily if I restart postfix, but it returns within a few cycles (the cron job runs every three minutes.
The error message repeats itself for each mail item that fetchmail parses. Here's the last bit of a fetchmail's results:
fetchmail: SMTP> RSET
fetchmail: SMTP< 250 2.0.0 Ok
fetchmail: not flushed
fetchmail: POP3> LIST 12
fetchmail: POP3< +OK 12 4337
fetchmail: POP3> RETR 12
fetchmail: POP3< +OK 4337 octets follow.
fetchmail: reading message [email protected]@mail.XX.com:12 of 12 (4337 octets)
fetchmail: SMTP> MAIL FROM:<[email protected]> SIZE=4337
fetchmail: SMTP< 250 2.1.0 Ok
fetchmail: SMTP> RCPT TO:<XX@localhost>
fetchmail: SMTP< 450 4.1.1 <XX@localhost>: Recipient address rejected: User unknown in local recipient table
fetchmail: SMTP error: 450 4.1.1 <XX@localhost>: Recipient address rejected: User unknown in local recipient table
fetchmail: SMTP> RSET
fetchmail: SMTP< 250 2.0.0 Ok
...fetchmail: not flushed
fetchmail: POP3> QUIT
fetchmail: POP3< +OK Bye-bye.
fetchmail: SMTP> QUIT
fetchmail: SMTP< 221 2.0.0 Bye
fetchmail: 6.3.8 querying mail.XX.com (protocol POP3) at Mon, 21 Jan 2008 18:58:12 -0500 (EST): poll completed
fetchmail: normal termination, status 0