Hi Larry,
Use default port 995 for POP3 over SSL.
SAP Note 856599 - FAQ: XI 3.0 / PI 7.0 / PI 7.1 Mail Adapter
You don't need to provide anything in the Communication Channel for SSL.
SOAP via SSL: Peer certificate rejected by ChainVerifier
Check these too:
Error on mail adapter : Peer certificate rejected by ChainVerifier
Can send my yahoo or gmail mail into a file
Regards,
Nabendu.