SMTP data timeout (message abandoned) on connection from

Hello,
looking in the exim_mainlog i see a quantity of

SMTP data timeout (message abandoned) on connection from

and always coming from the same bucket of domains.

tried to restart exim and this does not fix the problem. And I am also not sure that it could be a exim problem because emails coming from gmail or other external domains are properly delivered.

This could be a problem or misconfiguration of the sender?

I have also put the ips of the sender in a whitelist but it does not solve the problem.

The question is: it is the sender or exim causing the timeout?