Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

Can anyone explain what are the inbound and outbound relay in the mail server?

share|improve this question
Are you asking about specific settings in a mail system, or just general inbound/outbound relays? – Alex Jul 7 '10 at 23:38
What mail server are you referring to? – Justin Scott Jul 8 '10 at 0:58
Would be good to have answers for both general inbound/outbound relays and MS exchange specific inbound/outbound relays. – Ybbest Jul 8 '10 at 1:22
up vote 0 down vote accepted

An inbound SMTP relay can be seen as a firewall filtering data coming from outside, it receives emails that are destined to your domains and redirects them to your main mail server. It usually filters emails with a destination that is not one of your domains, or emails containing spam or viruses...

An outbound SMTP relay receives all the emails from your main mail server which are destined to the outside world and sends them to the appropriate outside mail servers. It can also filter emails that contain spam or viruses.

Be sure to read about Open mail relay and make sure that your relays are not open relays.

share|improve this answer
Thanks for your explanation. – Ybbest Jul 8 '10 at 4:46

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.