This is what has been learned:
1. Your address isn't a problem - you have received all my messages.
2. Your content filtering doesn't have any obvious problems so far.
3. Google treats a number of things as spam. Your spam filtering is tougher than my Gmail account.
4. You can receive email from non-google email servers.
5. You can receive messages from people not on your friends list or whatever google calls it.
6. You are receiving (presumably all) text mode messages.
You should have a gmail "All mail" folder to check. Make sure the emails aren't somewhere you haven't checked.
If there is no sign of the other members email (you apparently had other members send you email) within 5 days they should get "Undeliverable" messages:
Your message wasn't delivered because the destination email system rejected your message for security or policy reasons. For example, the email address might only accept messages from certain senders, or it might not accept certain types of messages, like those larger than a specific size.
Contact the recipient (by phone, for example) and work with them and their email admin to determine what policy or setting blocked your message and what you should do to make sure that future messages from you won't be rejected.…
If one of them could post the "source" message (the full email packet in text mode) I can figure out what the problem is.
I'm currently leaning toward some kind of content-based rejection since I haven't been able to get your mail system to reject me yet.