Exim fails to process emails and logs internal problem in system filter errors

Issue

On a cPanel/WHM server, Exim mail delivery is failing and the mail queue is growing with both pending and frozen messages. The Exim main log repeatedly reports errors similar to the following:

unable to set gid=979 or uid=985 (euid=47): system filter
internal problem in system filter: failure to transfer data from subprocess:
status=0100 readerror='No such file or directory'
Error in system filter: internal problem in system filter

Example log entries:

2026-07-17 11:37:33 1wjh82-00000006dXT-2tua unable to set gid=979 or uid=985 (euid=47): system filter
2026-07-17 11:37:33 1wjh82-00000006dXT-2tua internal problem in system filter: failure to transfer data from subprocess: status=0100 readerror='No such file or directory'
2026-07-17 11:37:33 1wjh82-00000006dXT-2tua Error in system filter: internal problem in system filter: failure to transfer data from subprocess: status=0100 readerror='No such file or directory'
2026-07-17 11:37:35 1wjh82-00000006dXG-1wkZ unable to set gid=979 or uid=985 (euid=47): system filter
2026-07-17 11:37:35 1wjh82-00000006dXG-1wkZ internal problem in system filter: failure to transfer data from subprocess: status=0100 readerror='No such file or directory'
2026-07-17 11:37:35 1wjh82-00000006dXG-1wkZ Error in system filter: internal problem in system filter: failure to transfer data from subprocess: status=0100 readerror='No such file or directory'

As a result, messages remain in the mail queue and Exim is unable to process them successfully.

Environment

• Imunify360
• cPanel

Cause

The development team confirmed that the issue is not related to Imunify360 Real-Time AV.

To verify this, the imunify-realtime-av service was disabled; however, the same Exim panic log errors continued to occur. This confirms that the issue persists independently of Imunify360.

The following error:

internal problem in system filter: failure to transfer data from subprocess: status=0100 readerror='No such file or directory'

is caused by an issue with the cPanel Exim system filter configuration or the cpaneleximfilter user/group configuration on the server, rather than any interference from Imunify360.