Hi, Some of my customers are complaining because they don't receive some emails. I have experienced the issue myself. I have checked the logs for the sender of an email I was waiting for. I found "relaylock" issues... I understand what relaylock is. It can be someone trying to send messages through my SMTP, or it could be a reject due to a block list. I have checked the sender smtp email address (126.96.36.199). It is not listed in any block list. Therefore, why do I get relaylock, when the final recipient is my own domain ??? or the customer domain... Could it be due to multiple IP addresses set in Plesk for the same mail server ? I mean, I have an IP for mydomain.com therefore, used also for mail.mydomain.com and I have a different IP address for mycustomerdomains.com used for mail.mycustomerdomains.com and the server hostname is something like "myserver.mydomain.com"... So, is there anything considered relay, when I get messages addressed to mycustomerdomains.com ?