Re: Postfix - Limit Bandwidth

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• In reply to: Ki Song: "Postfix - Limit Bandwidth"
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Date: Fri, 11 Nov 2005 13:15:23 +0000
To: fedora-list@redhat.com

Ki Song wrote:
> Is there a way to limit the bandwidth used by postfix when sending/receiving
> messages?
>
> The reason is that we sent out a newsletter, and the performance is
> excellent, but it is using up all our bandwidth.

I've not had to do this with Postfix, but I have with certain other
MTAs.

I assume your real problem is that it's slowing down other traffic,
especially interactive traffic. In my experience, using all *available*
bandwidth, in itself, is good. (You paid for that bandwidth: you might
as well use it).

And this is because most MTAs will open lots of outbound TCP/IP
connections if they have lots of mail to deliver. These connections will
swamp the other connections.

The best solution is probably traffic shaping *on the router* that will
prioritise other traffic over outbound SMTP. That isn't always
available.

As a "next best solution", I've found that limiting concurrent outbound
connections [1] makes MTAs co-exist much better with other network
services. I usually try three or four, and modify from there.

As far as I can tell, you can do this in Postfix by editing
/etc/postfix/master.cf, and changing
smtp unix - - n - - smtp
to something like
smtp unix - - n 4 - smtp

Note that with only one or two outbound connections, you can be slowed
down by bottlenecks elsewhere on the Internet, or if you are unfortunate
enough to connect to a misconfigured teergrube
(http://catb.org/~esr/jargon/html/T/teergrube.html).

Hope this helps,

James.

[1] i.e. limiting how many connections they have open at any one time

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• Previous message: hanpingtian_at_gmail.com: "Re: a problem about manual page's "`""
• In reply to: Ki Song: "Postfix - Limit Bandwidth"
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