Crossware Mail Signature app in an hybrid environment and Domino FP9. Apply IF2 or it will not work

A customer of mine uses the solution from Crossware to apply signatures to outgoing mails. I am helping them in moving users from on-premises Domino to Smartcloud Notes. The Crossware solution works in an hybrid environment, where the mail is routed through the on-prem server, but for us it did not work. After contacting Crossware Support, they told me that the SMTP bug introduced in FP9 breaks the functionality of their solution.

I applied FP9 IF2 to the on-prem server and it fixed the issue.