Postfix relay issue
I am trying to figure out relay in postfix .
When i check my mail log it shows that the outgoing mail goes through relay=abc.example.com but I don't see that in setup anywhere in postfix/main.cf and relayhost is empty ( relayhost = ) so where is it getting this relay address from ? I can setup relayhost to different relay mailserver ( relay = xyz.example.com )in main.cf and it will show that my outgoing mail changes to relay=xyz.example.com in mail log so where is this abc.example.com coming from when relayhost is empty in main.cf?? Thank you for your help.