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I have a mailing list application that sends emails through several dedicated SMTP servers (running Linux Debian 5 and Postfix) in the same network of a hosting company.

However, the application is using the servers' external IP addresses in order to connect to them over SMTP, and I was wondering what kind of improvement would be obtained if the application used the internal IP addresses of the servers instead?

Thank you in advance for your insight.

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migrated from May 25 '10 at 8:37

This question came from our site for professional and enthusiast programmers.

  • Ask the network admins
  • Check the routes. Do a traceroute. More hops can mean slower if the hops are used for connecting lots of subnets.
  • Test the latency. Do some pings. If the route is used much more than the others, it can be slower.
  • Test the throughput speed. Do some speedtests.

Be careful testing speed though: ask first if you're allowed to stress the network during daytime (work) hours...

Usually though, for sending an e-mail, using IP-address A or B won't be the bottleneck.

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Depending on the network compontents "between" the application and the (SMTP-)server (like firewalls, routers, switches...) it can differ a lot, but in most cases using the internal address should be faster.

This question is more a network question and should be asked to the people responsible for this specific network.

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