Mail with attachments stuck/held in mail queue

[Auron]

Hello

I usually manage to search for a solution but no luck this time...

For a few days now, any email being sent from my server that has an attachment is being held in the mail queue.
Mail sent locally is NOT having a problem only external recipients.

Mail without attachments or very small attachments does NOT have a problem.

Seems to be afffecting all users and to all destinations.

There also seem to be a number of different errors in the delivery logs with the main ones being:
SMTP timeout after sending data block (778032 bytes written): Connection timed out
or
Broken Pipe

Any help much appreciated.
Please let me know if any other info needed to help.

Regards
David

Cloudlinux 7.8.0 | cpanel 106.0.8 | CSF

 

[cPanelWilliam]

Hello!

Based on the error you reported, this sounds like a potential network issue. The main setting in Exim that would enforce attachment size would be the message_size_limit in the Exim configuration. With that said, this limit and the webmail attachment limit should not cause "Connection timed out" or "Broken pipe" errors, as those are indicative of network problems. I recommend reaching out to your service provider to see if they can troubleshoot the connection between your server and the recipient's server.

 

[Auron]

Thank you for your response

The message_size_limit = 50M and smtp_receive_timeout = 165s - so this should be ok.

Since posting this issue, I requested help from cPanel support who have had a look and also put this down to network issues.

The problem is I spoke with my datacentre earlier today and they claim there are no connectivity issues with my server so I am at a loss!

As it ONLY large emails with attachments that are being delayed / held in queue it is harder to locate the problem.
Obviously the email size is slowing down delivery and then causing the time-out but I cannot see where this is happening.

It is also happening email sent to all providers both public or private.

Can anyone suggest other ways to try and trace the 'blockage'!?

 

[cPRex]

When you mention this is happening to all providers, does the mail just sit in the queue and never get delivered? If you've had a ticket created and we've examined the mail logs on the machine, there isn't going to be any better details I can provide over the Forum than someone with direct access to the server.

In general, 50M seems like a very large email. I know both Gmail and Yahoo/ATT limit attachment sizes to 25M, so sending this file another way is likely the best solution.

 

[Auron]

The system keeps retrying to send the messages and they sit in the queue up to the maximum of 5 days and are then bounced back to sender.

Of course you are correct that someone with direct access can provide a more help as cPanel support have done. My problem has been that they have put it down to network connectivity issues and my datacenter have claimed there no connection issues with my server so I am stuck!

BUT

My provider have now informed me that they been experiencing high levels of DDoS attacks across their network for about a week now and this has caused their IP's to be blacklisted.
Their ASN has been blackilisted with UCEPROTECT-Level3 and while my server IP's are not directly listed they are affected.

I do not know for sure if this is causing the problems but until they resolve these issues there is no way of knowing.

Either way, I have found it very difficult if not impossible to find anyone who has suffered the exact same issue with outgoing mail, so once this has been resolved it will hopefully be helpful to others in the future.

 

[cPRex]

That could definitely cause the issue. If you'd like to submit a ticket to our team we could always check and confirm things on our end.