TLS error

imap 2.0.17, openssl 0.9.6d

Clients (Pine, Mulberry) connecting using STARTTLS generate messages like 
the one below. So it looks as though the server is looking for local 
certificates. SSL connections cause no such error message.

All seems to work but I would like to know why this happens. Since there 
seems to very little correspondence on this I suspect I have configured 
something incorrectly. Anyone else seen this?

imapd[17369]: [ID 432150 local6.error] TLS engine: No CA file specified. 
Client side certs may not work

Paul Christie
Bath University Computing Services