OK, I'm sure there is an easy answer to this question, but I cannot spot it .....
I am running sendmail 8.11.3 on an RS/6000 acting purely as a relay (receiving external Internet mail and passing it to the internal Exchange system).
The relay is correctly receving mail for the intended domains, and blocking all other domains. However, testing has shown that if an external user uses our domain name as the source address, with a destination address also in our domain the relay forwards this mail without question.
For Example:
Telnet relay 25
Helo mydomain.com
mail from: fakeuser@mydomain.com
250 sender ok
rcpt to: realuser@mydomain.com
250 recipient ok
data
You have been had ......
.
quit
This message is happily accepted by the relay and forwarded into the internal mail system.
How can I get the relay for accept mails with a source address of "@mydomain.com" provided that they also originate from my internal IP address range?
TIA
I am running sendmail 8.11.3 on an RS/6000 acting purely as a relay (receiving external Internet mail and passing it to the internal Exchange system).
The relay is correctly receving mail for the intended domains, and blocking all other domains. However, testing has shown that if an external user uses our domain name as the source address, with a destination address also in our domain the relay forwards this mail without question.
For Example:
Telnet relay 25
Helo mydomain.com
mail from: fakeuser@mydomain.com
250 sender ok
rcpt to: realuser@mydomain.com
250 recipient ok
data
You have been had ......
.
quit
This message is happily accepted by the relay and forwarded into the internal mail system.
How can I get the relay for accept mails with a source address of "@mydomain.com" provided that they also originate from my internal IP address range?
TIA