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I have a postfix server that i use to send auto responders and newsletters to subscribers. I know that major ISP's like hotmail and yahoo look for how many connections they get from an ip address. SO i want to know the following 1. how many connection does a postfix server opens ? 2. how many emails per connection does a postfix server send ? 3. how can i control the amount of connections to a specific ISP ?

Thanks

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You can get all the answers in www.postfix.org. –  Caterpillar Nov 28 '12 at 12:10
    
postfix.org/TUNING_README.html –  Caterpillar Nov 28 '12 at 12:10
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I know that major ISP's like hotmail and yahoo look for how many connections they get from an ip address.

HOW do you know this ?
Experience by many professional mail admins shows that they throttle senders solely based on the amount of mail they (try to) send in a given timeframe, not the amount of connections used.
One can still send 100 messages per second over one or two connections; the big ESPs will cut you off way before that point.

To answer your questions:

  1. This is controlled by default_destination_concurrency_limit, which defaults to 20 connections per destination
  2. Up to max_use messages will be sent over one connection, provided there are that many to send.
    For a single destination host, this will typically never be reached in one session.
  3. This involves several steps: first, create a new transport for each destination, and set its $destination_default_concurrency_limit, and next, route traffic to these transport using transport_maps.

You can find a wealth of information concerning such setups if you search the postfix mailinglist for "yahoo slow transport"

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