Problems receiving some emails

[Skie]

I've just recently set up a new server running CentOS 4.4 64bit with WHM 10.8.0 and cPanel 10.9.0-C117. My old server has the same version of WHM/Cpanel but uses RedHat 9 (yes, yes, I know, it's old. That's why I have the new server now).

I just received notice from a customer that they're not able to send email to themselves (or me as well). Yet, when we tested with the old server, it delivered just fine. Here's the bounce error that they're getting:

>>> Mail Delivery Subsystem <MAILER-DAEMON@unqualified.domain> 12/26/2006 11:32 AM >>>
The original message was received at Tue, 26 Dec 2006 11:32:52 -0600 (CST)
from host131.example.com [1.2.3.4]

  ----- The following addresses had permanent fatal errors -----
<me@myserver.com>
   (reason: 550-Callback setup failed while verifying <mycustomer@example.com>)

  ----- Transcript of session follows -----
... while talking to myserver.com.:
>>> DATA
<<< 550-Callback setup failed while verifying <mycustomer@example.com>
<<< 550-(result of an earlier callout reused).
<<< 550-The initial connection, or a HELO or MAIL FROM:<> command was
<<< 550-rejected. Refusing MAIL FROM:<> does not help fight spam, disregards
<<< 550-RFC requirements, and stops you from receiving standard bounce
<<< 550-messages. This host does not accept mail from domains whose servers
<<< 550-refuse bounces.
<<< 550 Sender verify failed
550 5.1.1 <me@myserver.com>... User unknown
<<< 503 valid RCPT command must precede DATA

Here's what /var/log/exim_mainlog says:

2006-12-24 16:31:26 H=(example.com) [1.2.3.4] sender verify fail for <mycustomer@example.com>: response to "MAIL FROM:<>" from example.com [1.2.3.4] was: 550 5.7.1 <>... Null Senders Not Accepted
2006-12-24 16:31:26 H=(example.com) [1.2.3.4] F=<mycustomer@example.com> rejected RCPT <me@myserver.com>: Sender verify failed

As best as I can tell, Exim is set up the same way on both servers. The only difference I can find in the exim.conf file is that the new server is using maildir and the old server is using mbox. However, what's confusing me is that the emails go through just fine when sent to the old server, but they're rejected when sent to the new server. If I disable the "Use callouts to verify the existence of email senders." option within Exim, then the email is delivered without any problems. However, I'm assuming this opens up my server/customers to more spam.

Any ideas?

[sparek-3]

Sender callouts is a form of sender verification. Basically any message sent to your server that has sender callouts enabled, the e-mail address that the message is sent from is checked to make sure that that address actually exists. This appears to be failing in this case.

from example.com [1.2.3.4] was: 550 5.7.1 <>... Null Senders Not Accepted

This is saying that the mail server for example.com (1.2.3.4) is not accepting mail from the null sender. The null sender is what is used to verify the validity of an e-mail address. Per RFC 1123's specs all mail servers have to accept mail from the null sender. This is seemingly a lot more common than I thought it would have been. Others may have different opinions, but in my view this is entirely at the fault of example.com (1.2.3.4) because they are not following RFC 1123 and accepting mail from the null sender. This needs to be brought to their attention. You can also check to see if this domain name is listed in the RFC Ignorant database:

http://www.rfc-ignorant.org

If a mail server is not accepting mail from the null sender then its conceivable that a lot of mail sent from that domain or even to that domain may not be reaching its intended recipient.

[Skie]

The sending server is a GWIA (Groupwise) in case anyone is familiar with it. However, if the problem is with their server, why did my old server accept any email from that particular server?

[sparek-3]

The old server probably does not perform a sender callout on new incoming mail.

Using sender callouts has its pros and cons. However, in any case the administrators of the server that is handling mail for the from address should really check the issue concerning the null sender. If they are not accepting mail from the null sender, then its very likely that a lot of mail sent from that domain is not reaching their intended destination.

[Lyttek]

Disable sender callout:

http://www.cpanel.net/docs/whm/Exim_...ion_Editor.htm

[Skie]

Disable sender callout:

http://www.cpanel.net/docs/whm/Exim_...ion_Editor.htm

I've done that for the time being, but I'd rather use it instead.

[mickalo]

It's interesting tho. We disable the "Sender Callout" recently as we noticed emails from this forum Cpanel Support, EV1 Support forum and few other Forums, their emails are rejected for failed sender callout verify. So it does have it's disadvantages.

just my 0.02 cents worth noting

Mickalo

[devGOD]

I've done that for the time being, but I'd rather use it instead.

did you ever fix this problem? i had to do the same thing... but i noticed on my old server I had it Call out turned on... So turning it off is just patching a problem that exist elsewhere. I want to find that other problem

[Skie]

did you ever fix this problem? i had to do the same thing... but i noticed on my old server I had it Call out turned on... So turning it off is just patching a problem that exist elsewhere. I want to find that other problem

Unfortunately, no I haven't. I've been concentrating on other issues and have not returned to this one.