Are you getting the error SMTP data timeout (message abandoned) on the connection from mail.xxxx.com.mx?

Users often get this error while sending emails with larger attachments.

But this also occurs due to incorrect handling of large packets by firewalls.

At Bobcares, we often get requests to fix SMTP errors, as a part of our Server Management Services.

Today, let’s see how our Support Engineers troubleshoot this SMTP error.

Why does the Exim log show SMTP data timeout error?

Customers often approach us when sending emails fails. Email errors are critical and they always need an immediate resolution.

So we check the log of the mail server. And the error message that appeared is SMTP data timeout (message abandoned).

That is, there was a timeout while trying to send the mail and the mail server discarded the mail. This can be due to many reasons.

A few common reasons our Support Engineers often see are larger attachment size, packet handling of firewall or router, or else the SMTP configuration.

Next, let’s see a few instances where we fixed this error.

How we fix the error SMTP data timeout (message abandoned)?

As the error shows up due to various reasons, first we check what caused the error in each case. Let’s see how we fix them.

Attachments with a larger size

Initially, we start troubleshooting by checking the log in the mail server. In Exim /var/log/exim_mainlog appeared as,

2020-01-28 18:05:05.672 [1061] SMTP data timeout (message abandoned) on connection from mail.xxxx.com.mx [2xx.78.xx.1xx]:23555 F=<xxx@yyyy.com.mx>

Upon checking we found that the mail had an attachment with 27MB. Hence it takes a longer time duration to check the mail content. This was higher than the smtp_receive_timeout. So the mail failed.

Hence our Support Engineers recommend reducing file size by zipping or compressing files and resend the mail.

Packet handling by the firewall

But in some cases, the user receives this error frequently. This can be due to incorrect handling of larger packets by the router/firewall.

There may be any restriction on the maximum size of the packet. So we need to configure the router to split it. The feature for this is known as path MTU discovery.

The misconfiguration of the MTU setting can cause an error while sending mail. So we correct it.

SMTP settings in the server

Similarly, SMTP settings in the WHM can block mail due to longer reading time. To avoid it we can enable a delay in the sending process.

For this we select, WHM >> Exim Configuration Manager >> Basic Editor.

Here in the ACL Options tab enable the option ‘Introduce a delay into the SMTP transaction for unknown hosts and messages detected as spam’. And this option appears as,

But enabling this option permanently allows sending of spam mail too. As it introduces a delay of a few seconds when it detects any spam mail to reduce inbound spam.

[Still, having trouble in fixing this SMTP error? – We can help you.]

Conclusion

In short, Exim logs the error ‘SMTP data timeout (message abandoned)‘ when the mail has an attachment of a larger size. This can also occur if the router is blocking larger packets. Today, we saw various ways our Support Engineers fix this error.