Question Email Queue Problem (emails from deleted domain)

[MerlinWoff]

Hi there,
We had a customer with a contact form which was misused for spaming. The domain from where the spam originated is now removed completly from our Plesk Server but new emails from this domain are created every some seconds and get inserted into the mail queue.

But all source files are removed!
How is that possible?

Thank you very much for enlightening us!

Best
Merlin