Comment # 3 on bug 1175637 from Wolfgang Bauer

Perhaps it should be added that those "unreferenced external files" do *not*
cause any problem. They are just unused and only take hard disk space
unnecessarily.

And another note: deleting mails is indeed unnecessarily slow, even without
bug#1173759. This has been improved recently in the git master branch:
https://invent.kde.org/pim/akonadi/-/commit/9eda8853c08b2b2eba6070ab16f27ffcaa857d46