I have just recently encoutered a funny prob with customer sending email to my email address domain.
Eg. Sender sends to me at firstname.lastname@example.org from their GMAIL account. Gmail sends them a note saying ...
Technical details of permanent failure: PERM_FAILURE: SMTP Error (state 9): 554 The IP Address of the sender (126.96.36.199) was found in a DNS blacklist database and was therefore refused.
Any idea what is wrong as the domain is a gmail domain and not mine and my customer is sending to me and not me sending to them. But when I try with my gmail I get that too but not when I try to send to my other personal email accounts.
I don't do any email marketing but it could be that my email sent out when my customers purchase or signs up.