I run into the same issue. bts calls $smtp->starttls() in line 2709, but starttls() in /usr/share/perl/5.38/Net/SMTP.pm line 621 calls die(). My mail server is using port 587 with STARTTLS. Thus, I dropped the starttls() call in /usr/bin/bts and all works well.
Regards, Daniel
signature.asc
Description: This is a digitally signed message part
