i'm getting a lot of 553 #5.1.8 Domain of sender address does not exist. I think its a dns problem, its just which? I have an SPF record.
the reverse of the ip matches the dns name of the mx record.
and i still get the bounces back
SMTP error from remote mail server after MAIL FROM:<email@example.com> SIZE=2255:
host : 553 #5.1.8 Domain of sender address <firstname.lastname@example.org> does not exist