Postfix - Limit Bandwidth
James Wilkinson
fedora at westexe.demon.co.uk
Fri Nov 11 13:15:23 UTC 2005
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
--
E-mail address: james | My friend, you would not tell with such high zest
@westexe.demon.co.uk | To children ardent for some desperate glory,
| The old Lie: Dulce et decorum est
| Pro patria mori. -- Wilfred Owen
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