I bought a certificate from Digital Signature Trust which is a well known certificate authority. The reason I bought my certificate, was so that email clients connecting to my imaps server wouldn't be bothered with warnings of unrecognized certificate authority as they would see with a self-signed server certificate. However, I haven't been able to configure dovecot with my Digital Signature Trust signed certificate so that the unrecognized certificate authority warning doesn't appear. I have the root certificate for Digital Signature Trust, but I don't know where to put it so that dovecot will use it. I tried appending the CA root certificate onto my server's certificate file with no success. The answer here is not, load my server's certificate into thunderbird or outlook express, because that is exactly what I'm trying to avoid by purchasing my certificate from a recognized authority. Help.

Before choosing a CA to buy certificate from you should've checked if their CA certificates come with thunderburd/outlook preinstalled. Seems like they are not, in which case you just wasted some money.