IMail - Error: Not a gateway; Not localhost, when I send mail to external addresses

Question/Problem: When I send mail to anywhere outside the IMail domains, I get an error message that says "not a gateway." I know the e-mail addresses are valid since I've sent mail to these addresses before.

Answer/Solution: This is usually due to the SMTP Security configuration (IMail Administrator | localhost | Services | SMTP | SMTP Security). You may have set the Relay Mail option to No Mail Relay. Or you may selected Relay Mail for Addresses without listing all the IP addresses and subnets that you wish to relay mail for. Be sure to stop and restart the SMTP service after a change.

Users who send from IP addresses that you do not list must set their mail clients to do an SMTP login ("My outgoing mail server requires authentication").

You can use the Addresses box and enter all the IP addresses of your client machines. You can enter class A, B, or C subnet forms in the Address box. For a class C address, just enter the Address as xxx.xxx.xxx.0 and Netmask of 255.255.255.0. For a class B address, 255.255.0.0.

See also:
IMail - Mail Relay Options

IMail Server 8.2 User's Guide - Security Strategies