Read receipt with @domain.invalid

I have installed an Sophos antispam system and I have connected it to Exchange Server 2013.

Everything work fine except the Read Receipt (the confirmation that you can ask when peolple read your mail).

When I send an email from my personal email address to my work email address, asking the Read Confirmation, I receive the confirmation but there is somithing wrong into the From field.

From: pippo@workmail.com on bealf of pippo@domain.invalid.

Has anyone ever seen this problem?

Thanks

Dario