If you set up mail server with machines IP address some xxx.xxx.xxx.xxx on a LAN and got the mails you send bounced back with error
mail for xxx.xxx.xxx.xxx loops back to myself
then the problem is that when you set up mail transfer agent using yast, you filled in the field 'Outgoing mail server'.
This field SHOULD BE LEFT EMPTY if your server has own permanent IP address and can send mail by itself.
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If you set up mail server with machines IP address some xxx.xxx.xxx.xxx on a LAN and got the mails you send bounced back with error
mail for xxx.xxx.xxx.xxx loops back to myself
then the problem is that when you set up mail transfer agent using yast, you filled in the field 'Outgoing mail server'.
This field SHOULD BE LEFT EMPTY if your server has own permanent IP address and can send mail by itself.