On 12/6/2014 3:39 PM, Whit Blauvelt wrote: > Hi, > > We have two ISPs, and a single Postfix server behind our Linux firewall that > gets NATed to in the same way from IPs on each of those ISPs' lines, with > both of those given in the MX records. After getting complaints that some > incoming mail was getting delayed by 5 or 10 minutes - sometimes much longer > - I sent a bunch of test mail from elsewhere, and saw that my test emails > all arrived either instantly or precisely 5 minutes late. > > Turns out one of the incoming lines times out on the response, which gets > logged on the sender but not the receiving system. Since most all mail is > only 5 or 10 minutes late - assuming the sending system behaves well and > goes to the next MX record in 5 or 10 minutes - it's not a particularly > visible problem - except for some sending systems that don't behave well, > which are out there. > > In telnetting to the two IPs, with the one that works the 220 line comes up > right away. On the bad line, the "Connect to" and "Escape character is '^]'" > lines come right up, but not the 220. If I then hit Enter the 220 line comes > right up, but not without that. > > Turning off tcp_window_scaling on receiver, sender, or both doesn't change > this. But the problem is specific to one ISP. Is this familiar to anyone? > > Thanks, > > Whit >
This sounds like a problem in the router or external firewall, not postfix or the box postfix is running on. A tcp recording may give some insight... or maybe not. http://www.postfix.org/DEBUG_README.html#sniffer -- Noel Jones
