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I'm writing a ruby script to process incoming email for a specific email address using a transport.

Postfix transport table      ruby-script

Postfix master file
ruby-script unix    -   n   n   -   -   pipe
      flags=    user=zimbra argv=/usr/bin/ruby  /opt/zimbra/ruby-script.rb

Let's say 10 emails are piped to the ruby script within the same timeframe. Does postfix create 10 ruby-script.rb processes to handle those 10 emails or how does it work?

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up vote 2 down vote accepted

Yes, postfix will spawn a new process for each.
But you can control the parallel delivery with ruby-script_destination_concurrency_limit=2 for example, meaning 2 parallel delivery to ruby-script transport.

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if I set the limit to 2 what happens with the other 8 emails? Are they bounced back to the users? – joshu May 15 '13 at 18:46
No, they are queued up until the running scripts finish up. – Sandor Marton May 15 '13 at 18:48
Great thanks for explaining! – joshu May 15 '13 at 20:01

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