That's the reason, then. By design, Deb-o-Matic forwards mails to the email listed in GPG signature, to avoid spamming mail addresses which are not directly involved in unofficial package builds. Having GPG support disabled prevents creating any email message.
Documentation lacks this information (and a lot of things in general), but I'm going to write a new, complete, Deb-o-Matic user's guide which will also consider this aspect, which could be confusing. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org