Jeremy,
I have a new group that ha a member receiving the following return
when he posts, either text or phots, to the group:
I assume you mean when he posts a message, whether it contains only text or has photos. Because I don't think he'd get any return just from uploading a photo on site.
How do I stop this message? He¡¯s using an email address from his own
domain.
I don't think you can do anything about it, it is something between him and the service he's using to receive his emails.
I think what's going on is that when he posts a message to Groups.io his message is sent back to him, with the group footer appended & etc. His email service sees that message, which says it was From him, but was actually sent by some other service. So in that strict sense they are correct: Groups.io "spoofed" the member's address into the From of the posted message.
Maybe there's a setting he can use to "white list" Groups.io as a sender, or maybe he needs to contact his service's tech support and ask them how to avoid this message when using mailing lists. Most mailing lists (including Yahoo Groups, pre-DMARC) would do the same thing so it is something they ought to know about and be able to handle.
Either that or they don't want to support customers who use mailing lists, and he should take a hint.
Shal
Shal Farley