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Mail server reports “550 Address unknown”, but check via telnet finds the address

Christian Buerger

Hello,

I'm trying to send an email through Postfix from mydomain.com to an address I know exists (info@example.org) - the receiving end seems to be running a Sophos product.
Postfix is reporting that the address does not exist.

Excerpt from my mail log

Jun 7 07:01:47 mydomain postfix/smtp[50352]: 010BB40606: to=<info@example.org>, relay=remote.example.org[redacted]:25, delay=1.2, delays=0.37/0/0.37/0.48, dsn=5.0.0, status=bounced (host remote.example.org[redacted] said: 550 Address unknown (in reply to RCPT TO command))

Here is the telnet session (from the server where Postfix runs) showing that the address exists:

# telnet remote.example.org 25
Trying [redacted]...
Connected to remote.example.org.
Escape character is '^]'.
220 sophos.example.local ESMTP ready.
HELO mydomain.com
250 sophos.example.local Hello mydomain.com [redacted]
MAIL FROM: <myaddress@mydomain.com>
250 OK
RCPT TO: <info@example.org>
250 Accepted

To me it looks like my email is rejected by Sophos for some reason. From what limited information I could gather so far, it seems to be related to "recipient verification". 

Could someone help me understand what kind of check the other side is running that keeps my email from being delivered? The email address I'm sending from and the address in the return path do exist (which can be checked by using telnet). 

Thanks!



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  • 0

    Hi,

    your first attemp to send the email is "bounced".. its a normal protection agains spammers.

    da ich denke du bist deutsch:

    https://de.wikipedia.org/wiki/Bounce_Message

     

    greets

    zaphod
    ___________________________________________

    Home: Zotac CI321 (8GB RAM / 120GB SSD)  with latest Sophos UTM
    Work: 2 SG430 Cluster / many other models like SG105/SG115/SG135/SG135w/...

  • 0 in reply to zaphod

    I've tried it several times and the email bounces each time.

    For spam protection messages sometimes are greylisted and get the status "deferred", they are then retried later on. This seems to be not the case here, the message is bounced and will thus not be send again unless the user initiates a new mail.

  • 0 in reply to Christian Buerger

    bounce is a simple protection agains spammers... first mail from a source-mail server will be bounced... cause per default all mail servers will send a message after some time again...

    its a technical trick to get out the spams from dial-up host.. they will not retry to send...

    mailservers should send mails to other mailservers... users should use some internal mail servers or servers they have authenticated to so the server will then never bounce such a mail...

     

    greets

    zaphod
    ___________________________________________

    Home: Zotac CI321 (8GB RAM / 120GB SSD)  with latest Sophos UTM
    Work: 2 SG430 Cluster / many other models like SG105/SG115/SG135/SG135w/...

  • 0 in reply to Christian Buerger

    Hi, Christian, and welcome to the UTM Community!

    This doesn't seem like a soft bounce, more like a solid statement that the account you're trying to send to doesn't exist.  Does the account name have an Umlaut in it?  Is it possible that your Postfix configuration sends that incorrectly?  Have you contacted the recipient to ask him to have his UTM admin send you the log lines from their rejection?

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
Reply
  • 0 in reply to Christian Buerger

    Hi, Christian, and welcome to the UTM Community!

    This doesn't seem like a soft bounce, more like a solid statement that the account you're trying to send to doesn't exist.  Does the account name have an Umlaut in it?  Is it possible that your Postfix configuration sends that incorrectly?  Have you contacted the recipient to ask him to have his UTM admin send you the log lines from their rejection?

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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