Not sure if this is due to security; hence the reason i am asking here. I have 2 SMTP server and a couple of unix servers

  1. the actual mailserver running on window. client connect to it and download mail.
  2. a postfix SMTP server running in one of the unix box use for relaying mail to 1).

We call my mailserver MTA1 and the POSTFIX server MTA2

I am a novice in mail and i realize these following different flows when some of the different unix servers are sending mail to the public

They can either

  1. unix server (mailx) --> (localhost-sendmail) ---> MTA2(postfix) --> MTA1 (actual mailserver) --> external MTA

  2. unix server (mailx) --> MTA2(postfix) --> MTA1 (actual mailserver) --> external MTA

  3. unix server (mailx) --> MTA2(postfix) --> external recipient MTA

  4. unix server (mailx) --> MTA1 --> external recipient MTA

  5. unix server (mailx) ---> (localhost-sendmail) --> external recipient MTA directly ?

q1) Is all the above paths valid ? If so, what should be the correct way ?

q1) Notice 1), not sure why there is a sendmail listening on localhost when the MUA can go directly to MTA2 or MTA1 (like path2)

q2) Notice 2) not sure why the need for MTA2 to relay to MTA1 when they can go the 3) path

q3) Notice 3) not sure why the need to go to MTA2 when they can go to MTA1 also

q4) Notice 5) i have a strong feeling i can send to the sendmail on localhost and have it send to the external MTA directly.

So which is the right path ?

  • I'm not seeing the threat you want to counter. You put mail servers in when you need the service they provide. I'm confused about what your question is. – schroeder Apr 5 '17 at 13:31
  • @schroeder i am asking if the above listed paths are valid ? if they are all valid, why can't we choose the shortest path ? is there any security reason why a path is setup this way – Noob Apr 5 '17 at 14:44
  • define "valid" though - are you asking why the email admin set up the network that way? – schroeder Apr 5 '17 at 14:46
  • @schroeder yea just thinking why so many diff paths, which would be the correct one or is there any security concern for setting so – Noob Apr 5 '17 at 15:45

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