I've reopened this bug because of two things: a) the priority of bsd-mailx was lowered[1] to optional in 2016 (Robert, can you comment on that?)
b) consequently, mailutils is now being installed by default in stretch and it doesn't respect /etc/mailname - #253513[2] Regards, Daniel 1. https://anonscm.debian.org/cgit/users/robert/bsd-mailx.git/commit/?id=94629511972c3da0954522828582f581b80615ba 2. https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=253513
