ISO builds are broken by weird enigmail situation

Originally created by @intrigeri on #13530 (Redmine)

It seems that our build system is trying to install 2:1.9.8.1-1~deb9u1 from stretch/updates, that depends on Thunderbird 52 while we still ship Thunderbird 45. If that was the only problem, then the obvious solution is to upload 2:1.9.7-2 to our custom APT repo.

But https://tracker.debian.org/pkg/enigmail doesn’t know about 2:1.9.8.1-1~deb9u1, http://metadata.ftp-master.debian.org/changelogs/main/e/enigmail/enigmail_1.9.8.1-1~deb9u1_changelog gives me a 404, and rmadison doesn’t know what’s going on either, so I wonder what’s going on.

Feature Branch: bugfix/13530-enigmail-compatible-with-thunderbird-45

Related issues

• Related to #12639 (closed)
• Blocks #13234 (closed)
• Blocks #11738 (closed)