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From what I can tell, the RFC's only specify that you should wait for the initial response for 5 minutes. But I can't find anywhere where it says how long to wait for the TCP connection to be setup.

They are running what appears to be some mail server on Windows, which seems to have a default timeout of 20 second. I note that an interactive protocol like HTTP seems to have an initial connect timeout of around 60-90 seconds. I would think SMTP, being a non-interactive service would be at least that long or longer, but I'm being told:

FYI the last 6 delivery failures. Oct 16 (x2), 17, 18(x2, spaced) and 20. Your upstream mail server is down/unavailable a LOT.

(I wholly expect this one to end up in the retry queue as well)

Please do something about this.

and that the following demonstrates that my email service is "offline" or

 Thu 2015-10-15 23:43:50: Resolving MX records for [xxx.org] (DNS Server: 129.250.35.250)...
 Thu 2015-10-15 23:43:50: *  P=010 S=000 D=xxx.org TTL=(176) MX=[mx1c25.carrierzone.com]
 Thu 2015-10-15 23:43:50: *  P=020 S=001 D=xxx.org TTL=(176) MX=[mx2c25.carrierzone.com]
 Thu 2015-10-15 23:43:50: *  P=050 S=002 D=xxx.org TTL=(176) MX=[mx3c25.carrierzone.com]
 Thu 2015-10-15 23:43:50: Attempting SMTP connection to [mx1c25.carrierzone.com:25]
 Thu 2015-10-15 23:43:50: Resolving A record for [mx1c25.carrierzone.com] (DNS Server: 129.250.35.250)...
 Thu 2015-10-15 23:43:50: *  D=mx1c25.carrierzone.com TTL=(5) A=[64.29.145.41]
 Thu 2015-10-15 23:43:50: Attempting SMTP connection to [64.29.145.41:25]
 Thu 2015-10-15 23:43:50: Waiting for socket connection...
 Thu 2015-10-15 23:44:12: *  Winsock Error 10060
 Thu 2015-10-15 23:44:12: *  64.29.145.41 added to connection failure cache for 5 minutes
 Thu 2015-10-15 23:44:12: Attempting SMTP connection to [mx2c25.carrierzone.com:25]
 Thu 2015-10-15 23:44:12: Resolving A record for [mx2c25.carrierzone.com] (DNS Server: 129.250.35.250)...
 Thu 2015-10-15 23:44:12: *  D=mx2c25.carrierzone.com TTL=(5) A=[64.29.145.46]
 Thu 2015-10-15 23:44:12: Attempting SMTP connection to [64.29.145.46:25]
 Thu 2015-10-15 23:44:12: Waiting for socket connection...
 Thu 2015-10-15 23:44:33: *  Winsock Error 10060
 Thu 2015-10-15 23:44:33: *  64.29.145.46 added to connection failure cache for 5 minutes
 Thu 2015-10-15 23:44:33: Attempting SMTP connection to [mx3c25.carrierzone.com:25]
 Thu 2015-10-15 23:44:33: Resolving A record for [mx3c25.carrierzone.com] (DNS Server: 129.250.35.250)...
 Thu 2015-10-15 23:44:33: *  D=mx3c25.carrierzone.com TTL=(5) A=[64.29.145.47]
 Thu 2015-10-15 23:44:33: Attempting SMTP connection to [64.29.145.47:25]
 Thu 2015-10-15 23:44:33: *  64.29.145.47 in connection failure cache for up to 5 minutes due to previous connection failure(s)

But either no one else takes the time to send me any notification about failures, or this is the only mail server that is having a problem communicating to my email provider.

At this point, I don't know what my next step should be, since most timeouts in sendmail are in the 1-5 minute range (most seem to correspond to RFC guidelines), but I'm told that 20 seconds is more than enough for a server to wait for an initial connect to a busy mail server.

Am I overlooking someplace where the initial connect timeout is specified, or is it the case that a sender MTA can use anything they want for the initial TCP connect timeout?

FWIW, I'm hoping this is the right forum -- since it's entirely in the server-to-server communication realm.

Thanks!

  • I can connect to your mail servers within two seconds. The problem is most likely at their end, not yours. – Michael Hampton Oct 22 '15 at 1:55
  • 64.29.145.46 and 64.29.145.47 are not responding on port 25 or to ping for me. And yes, 20 seconds is definitely more than required for a smtp response. Mail servers could run into problems if they allowed connections to take too long. – Ryan Babchishin Oct 22 '15 at 3:13
  • Interesting difference -- 1 person connects in under 2, another person gets no response. !? Wazzup with that? I've never had such a wide variation in connectivity. @Ryan -- what problems? If the timeout is 5 minutes for the initial response, what problems could there be if the delay was in TCP connect, or a slow response after connect? – Astara Oct 22 '15 at 5:42
  • If the server connects to a bunch of slow systems like you, and waits 5 mins for a timeout for each one, it could end up with lots of processes/threads doing nothing, for no good reason. Which could prevent the server from making any more outgoing connections (because there are usually limits). – Ryan Babchishin Oct 22 '15 at 6:17
  • The 5 minute timeout is from the mail RFC's -- and is described as the minimum a server should wait before first response. There is no breakdown below that as far as how much one should wait for a TCP connect. Considering that some can connect in 2 seconds and some > 20 seconds, it seems like there's a wide variation (which seems odd). – Astara Oct 22 '15 at 16:27

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