Same issue,debian edition pro 6.2.4.
But it'll work if the sent mail is a register,ignoring the head of mail is:
Account activation on 127.0.0.1:8000.
Without any configuration change,it just don't show like:
Account activation on seafile.mydomail.com.
But in the version of 6.1.9 pro,it can send me a normal thing like above.
Seafile,in love you and bothered by you too...