When doing porter uploads, one must not forget to pass -m"My Name <email@example.com>" to dpkg-buildpackage, e.g. with --debbuildopts for cowbuilder. Thanks Aurélien and sorry to everyone who got the upload mails.
(How are the rules for sponsored uploads? I get conflicting info on these, and indeed, the one I sponsored never showed up on my QA DDPO page…)