You can ignore messages, they are actually good (and fixing a long-standing problem we had).
Let me explain why:
Lots of listadmins have had their membership disabled due to "bounce going over threshold" (see this mailing list for lots of people complaining). The issue is simple. Lots of spammers send spam or virus or phishing emails to *-owner@ which mailman happily forwards to listadmins. But your server (e.g. Gmail), actually rejects those emails (some go to spam but lots of them don't even get accepted) and with the rejection notice, mailman (also happily) increases your bounce score and disables your membership if it passes the threshold.
What we did to fix it is that once you pass the threshold, mailman sends a probe email to your account and if that gets received then it doesn't disable your membership (hopefully reduces your bounce score, but not sure) and the server rejects the probe mail, then mailman disables the account for good.
TLDR: Don't worry, it's okay.
HTH