Where Does The MTA Keep The Message Data Until It Knows Where To Enqueue? (Doc ID 1945530.1)

Last updated on MARCH 30, 2022

Applies to:

Goal

It is convenient to think the tcp_smtp_server process writes the message directly to the destination channel queue as it receives the data, but that gross over-simplification can lead to under configuration of memory/swap on MTA systems -- or over commitment via the MAX_PROCS and MAX_CONNS dispatcher config options -- which can lead to unexpected system memory/swap shortage and processes randomly crashing.

So if it does not immediately write the data directly to the destination channel queue directory, where does the MTA store the message data as it is receiving it?

What limits can prevent the MTA from consuming all system memory holding such data -- causing "unix: WARNING: /tmp: File system full, swap space limit exceeded" messages?

Solution

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