Hi,
Because this came up for at least one of the users of the Einstein Toolkit mailman email lists, I think it would be good to spread the "solution".
The symptom that user saw was that their own posts to the mailing lists didn't show up in their own INBOX. There is a mailman setting that could disable posts back to the sender, but that wasn't the issue here.
The issue in the end was that the email provider was gmail (even though the domain appears differently):
If you have a mailing list that includes subscribers using gmail, a copy of messages they send to the list won’t appear in their own Gmail “Inbox”. It only shows in “Sent Mail” or “All Mail”.
This is a problem on the Gmail end. The list server correctly delivers the message to the gmail.com servers, but Gmail discards it. According to Gmail:
Mail you send to a mailing list you subscribe to will only appear in "Sent Mail". Gmail automatically skips your Inbox and archives the message to save you time and prevent clutter. The message will appear in your Inbox if someone responds to it or if there is an error delivering the message. If you'd like to view your message, you can find it in Sent Mail or All Mail.
You can find more information about this on this Gmail help page:
https://support.google.com/mail/answer/8824?rd=1
There is no way to avoid this problem, unfortunately. It's something Gmail controls, not the list server.
Frank