Hi.
I also have this problem, in my case with sendmail, but that is what I believe Horde uses.
Oct 21 19:15:45 SERVERNAME sendmail[3041]: STARTTLS=client, error: connect failed=-1, SSL_error=1, errno=0, retry=-1
Oct 21 19:15:45 SERVERNAME sendmail[3041]: STARTTLS=client...