What's up, folks. I've been banging my head against the wall for awhile with this one. Ok, so I have an email configuration using Postfix and Courier, which seems to be up and running ok. Messages are being sent, but some servers are bouncing them back to me saying the user does not exist. For example

This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

 jedi@ricketycontraption.com
   No Such User Here

------ This is a copy of the message, including all the headers. ------

Return-path: <usr@domain.com>
Received: from [24.42.78.153] (helo=[10.0.1.2])
   by fst02.justhost.com with esmtp (Exim 4.69)
   (envelope-from <usr@domain.com>)
   id 1OFtsZ-00056J-MV
   for jedi@ricketycontraption.com; Sat, 22 May 2010 13:56:59 -0500
From: Ro <usr@domain.com>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Subject: testing
Date: Sat, 22 May 2010 14:56:59 -0400
Message-Id: <F9D2F64A-C67D-4B1E-AE4C-12FF7AD12EEF@domain.com>
To: jedi@ricketycontraption.com

I've checked my mx records, which point to the correct place, updated my DNS, set my reverse DNS a couple of days ago to give it time to propogate, and still nothing. I'm not getting any mail errors or warnings and all of my mail domain urls are matching up. Here is an excerpt from my mail logs which.

May 22 15:11:34 durendal postfix/qmgr[2774]: 57631A697: from=, size=1307, nrcpt=1 (queue active)
May 22 15:11:34 durendal amavis[2216]: (02216-01) Passed CLEAN, LOCAL [127.0.0.1] [24.42.78.153] -> , Message-ID: <2c10138d88150a94db3e88b4e0a27eae.squirrel@ricketycontraption.com>, mail_id: 4lVSxyNpDdgq, Hits: -0.999, size: 792, queued_as: 57631A697, 436 ms
May 22 15:11:34 durendal postfix/smtp[2894]: B1DD2A696: to=, relay=127.0.0.1[127.0.0.1]:10024, delay=0.71, delays=0.23/0.04/0.01/0.43, dsn=2.0.0, status=sent (250 2.0.0 Ok, id=02216-01, from MTA([127.0.0.1]:10025): 250 2.0.0 Ok: queued as 57631A697)
May 22 15:11:34 durendal postfix/qmgr[2774]: B1DD2A696: removed
May 22 15:11:34 durendal imapd: LOGOUT, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], headers=0, body=0, rcvd=660, sent=203, time=0
May 22 15:11:34 durendal imapd: Connection, ip=[::ffff:127.0.0.1]
May 22 15:11:34 durendal imapd: LOGIN, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], port=[45997], protocol=IMAP
May 22 15:11:34 durendal imapd: LOGOUT, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], headers=1710, body=0, rcvd=296, sent=4010, time=0
May 22 15:11:34 durendal postfix/smtp[2904]: 57631A697: to=, relay=playvicious.com[69.175.25.18]:25, delay=0.35, delays=0.03/0.01/0.26/0.05, dsn=5.0.0, status=bounced (host playvicious.com[69.175.25.18] said: 550-Verification failed for 550-No Such User Here 550 Sender verify failed (in reply to RCPT TO command))
May 22 15:11:34 durendal postfix/cleanup[2892]: B2A8AA698: message-id=<20100522191134.B2A8AA698@durendal.ricketycontraption.com>
May 22 15:11:34 durendal postfix/bounce[2907]: 57631A697: sender non-delivery notification: B2A8AA698
May 22 15:11:34 durendal postfix/qmgr[2774]: B2A8AA698: from=<>, size=3592, nrcpt=1 (queue active)
May 22 15:11:34 durendal postfix/qmgr[2774]: 57631A697: removed
May 22 15:11:35 durendal postfix/pipe[2908]: B2A8AA698: to=, relay=maildrop, delay=0.34, delays=0.18/0.01/0/0.15, dsn=2.0.0, status=sent (delivered via maildrop service)
May 22 15:11:35 durendal postfix/qmgr[2774]: B2A8AA698: removed
May 22 15:11:36 durendal imapd: Connection, ip=[::ffff:127.0.0.1]
May 22 15:11:36 durendal imapd: LOGIN, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], port=[45998], protocol=IMAP
May 22 15:11:36 durendal imapd: LOGOUT, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], headers=2026, body=0, rcvd=296, sent=4545, time=0
May 22 15:11:38 durendal imapd: Connection, ip=[::ffff:127.0.0.1]
May 22 15:11:38 durendal imapd: LOGIN, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], port=[45999], protocol=IMAP
May 22 15:11:38 durendal imapd: LOGOUT, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], headers=0, body=2556, rcvd=178, sent=3996, time=0
May 22 15:13:42 durendal imapd: Connection, ip=[::ffff:127.0.0.1]
May 22 15:13:42 durendal imapd: LOGIN, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], port=[46004], protocol=IMAP
May 22 15:13:42 durendal imapd: LOGOUT, user=jedi@ricketycontraption.com, ip=[::ffff:127.0.0.1], headers=0, body=0, rcvd=87, sent=391, time=0
May 22 15:15:02 durendal imapd: Connection, ip=[::ffff:127.0.0.1]
May 22 15:15:02 durendal imapd: Disconnected, ip=[::ffff:127.0.0.1], time=0

I'm so close to getting this to work as it seems to send to gmail fine, but only craps out on particular servers that require verification.

And does that user actually exist?

Network-tools.com doesn't think so

Validation results

canonical address: <jedi@ricketycontraption.com>

MX records
preference    exchange    IP address (if included)
10    mail.ricketycontraption.com    [69.164.218.253]
SMTP session

[Contacting mail.ricketycontraption.com [69.164.218.253]...]
[Connected]
220 durendal.ricketycontraption.com ESMTP Postfix (Ubuntu)
EHLO Network-Tools.com
250-durendal.ricketycontraption.com
250-PIPELINING
250-SIZE
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH PLAIN LOGIN
250-AUTH=PLAIN LOGIN
250-ENHANCEDSTATUSCODES
250-8BITMIME
250 DSN
VRFY jedi
550 5.1.1 <jedi>: Recipient address rejected: User unknown in local recipient table
RSET
250 2.0.0 Ok
EXPN jedi
502 5.5.2 Error: command not recognized
RSET
250 2.0.0 Ok
MAIL FROM:<admin@Network-Tools.com>
250 2.1.0 Ok
RCPT TO:<jedi@ricketycontraption.com>
250 2.1.5 Ok
RSET
250 2.0.0 Ok
QUIT
221 2.0.0 Bye
[Connection closed]

I set it up with ispconfig3 and I am able to log in and send messages from it, so I know it exists. Why it is not being resolved as so seems to be the mystery.

Looks like the email address is valid to me.

AreOh, look in your logs around the time the email from 24.42.78.153 failed to see if there is something there helpful. Outside of that, I don't know what else to tell you at this point.

I've been doing some reading, the problem may have something to do with my SPF record. As soon as it propagates, I'll try it again. It seems to be isolated to a few servers here and there, but I would rather solve the root of the problem as opposed to just rolling the dice when I send out email.

I just needed to fix my SPF records on my server. Once it was updated and propagated, it worked like a charm.