[Mailman-Users] Approved postings are not being delivered

Hi, I moderate and administrate a professional discussion list with about 6,000 subscribers. Most of the subscribers use Gmail, Yahoo, or other free email services. In the recent past, approved list postings are not being delivered to Gmail and Yahoo.

I have subscribed to the list using my Gmail, Yahoo, and official email ids. I receive approved list messages only to my official email id, but not to my other two email ids. Our network support team tells me that the issue is because of the blacklisting of the email relay host used for mailing list service. Can someone help me to resolve the issue?

I'm using Mailman 2.1.20

Thanks, Francis