[Dovecot] SSL CA root certificate

[Mail Admin]

In reading through the mailing list, this question seems to have come up
before, but never quite answered.

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.

Thanks,
Derek