sendmail's outgoing IPs

[Ian Smith]

On Sun, 15 Jun 2008 Wojciech Puchar <wojtek at wojtek.tensor.gdynia.pl> wrote:

 > no i'm not a spammer, but my users often send mails like 20-40MB sized.
[..]
 > something like "T1" here costs far too much to dedicate it just for mails.
 > 
 > for the same price i can get four "4Mbit/s" ADSL's (which i have now), 
 > that actually gives 4Mbit/s download speed, but only 512kbps upload.

Lucky you.  We have a 1500/256kbps link for up to 20 boxes, though
there's talk of upgrading to (nominally) 8M/384kbps.

 > if you substract ACK's needed for 4Mbit/s download, little is left.

Slight exaggeration, though TCP downloads do need say 5-10% of download
bandwidth upstream.  Sure, as soon as you use all upload bandwidth (your
mail example, torrents of course, youtube uploads etc) your download
bandwidth is shot.  Not to mention very soggy remote ssh access :) 

 > my ipfw rules manages all this so web browsing works fine, but mail output 
 > is a problem now.

Why not add dummynet pipes and suitable rules to limit the outbound
bandwidth for mail (or torrents, whatever's a problem) to a maximum of
say 80% of upload, so for 512k set upload limit to maybe 400k, leaving
plenty of room for TCP acks?  So mail takes a bit longer to send ..

You can get fancier with weighted queueing of course, I haven't tried. 

Works well here anyway, but we're not running a multilink connection. 

hth, Ian