[Dovecot] ssl cert for mail server

for testing a new ssl cert. it works ok for browsers, but

openssl s_client -crlf -connect ms1.trailsandtribulations.net:443

=> verify error:num=19:self signed certificate in certificate chain

is this ssl cert - as it's constructed - is ok for mail clients? (realize needs to be on mail port etc - right now talking about the cert itself.) have had problems with thunderbird, and was wondering if this might be part of the problem.