[CentOS] fetchmail log messages I don't understand

I see these messages every time fetchmail pops my mail.  I don't understand
what certificates it is talking about, or how to straighten this out.

fetchmail: Server CommonName mismatch: localhost != mail.mydomain.com
fetchmail: Server certificate verification error: self signed certificate
fetchmail: Server certificate verification error: certificate has expired

What do I need to read up on to understand this and find a fix?

TIA,
-chuck