I have been noticing that my email posts on one of the Google Groups I am subscribed to do not get replies from other members anymore. I was starting to get upset and thought my popularity has dropped and people are totally skipping my emails! I asked Mahmoud what was the last email he got from me and he told me it was several days ago! I logged in to the group website and found that my recent posts do NOT get delivered at all, without a single notice from Google!

After several tests I came to the following:
When your subscription in Google Groups is on email A, you have to really send from this email account A. If you use an email account B with an alternate account A (that appears in the From field), this will not work (as of May 29th and at least for me!)
You will not even get a delivery error from Google in this case because they think you are forging this email.

However, if you send from a totally different account C (and don't try to modify the sender), you will get a delivery error.

Moreover, if you send from account A USING ANY ALTERNATIVE ACCOUNT B, C, D, ... The message will be delivered!

Bottom line, now they only look for the real sender, and if an alternative account is used, they don't reply back with any error.