Several customers reporting that they haven't received emails that were sent from C4C

[samirv]

Dear SAP Experts,

We have several reports from our customers that for a number of emails sent from us from within c4c "that they have not recived an answer from us". We don't currently know whether these emails actually went into the customers spam/junk or if they were not delivered at all.

I have checked :

1. DKIM and DMARC were already in place at the time that the emails were sent.
2. DKIM/DMARC/SPF currently pass.
3. On the case/ticket there is no indication that the email was "bounced" and the bounced indicator in activies->emails = false.
4. I have tested sending emails to my email from the same channel in c4c and all received without issue.

Has anyone else had experience of this and if so, what was the cause and/or resolution.  Thanks,

Samir

(fyi I have also reported to SAP via incident in parallel with full details of a specific example for them to check the delivery, but from my experience that will usually take a lot of hard work and time and I may not get a meaningful response from them in the end so asking here in parallel).