Will MTA iterate over MX to find a user?

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horon_ekb2016-03-16 21:57:42

Mail server

horon_ekb, 2016-03-16 21:57:42

Given: There are MX servers A (priority 10) and B (priority 20), on server A there are users Masha and Petya, and on server B there is a user Vasya (but he is not on server A).
Question: MTA, when trying to deliver a letter to Vasya , will hit MX with a lower priority number, there is no user (he is on server B), will MTA go to server B to look for a user, or will he immediately give a whack that the user was not found? Expand the topic if possible.

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2 answer(s)

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Vladimir Dubrovin, 2016-03-16
@horon_ekb

A server with a weight of 20 will be contacted only if a server with a weight of 10 is network unavailable.
If the weight is the same, then everything will depend on what error code the recipient's server returns with a non-existent user. If 5xx (which is the most common behavior) there will be no retry, if 4xx there will be a retry and _randomly_ a different server may be selected. As a result, there is a chance that someday the letter will be delivered.
If you are thinking about whether it is possible to separate users across servers in this way, then no, you can’t. This is organized by separating the front-end and back-end servers.

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TyzhSysAdmin, 2016-03-17
@POS_troi

Since I was pinged, I must unsubscribe :)
horon_ekb fully answered the question.