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Re: Timeout after end of SMTP data lines and ".<cr><lf>"

  •  05-17-2010, 13:43

    • Supur is not online. Last active: 12-09-2018, 12:59 Supur
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    Re: Timeout after end of SMTP data lines and ".<cr><lf>"

    Dear Thomas,

    Many thanks for these suggestions. I will comment my configuration first:

    Mercury server is installed on PC with Asus A7V8X-X mainboard:

    • VIA KT400 Northbridge
    • VIA VT8235 Southbridge
    • VIA Rhine II Fast Ethernet Adapter (Realtek 10/100 Mbps Ethernet PHY)

    So, "NVidia NForce 4" is not used, I think that's for sure. Furthermore, I do not use integrated VIA NIC but have additional NIC "D-Link DGE-528T Gigabit" PCI card for that. Anyway, I disabled "Checksum offload" option on D-Link NIC (it used to be set originally to "Tx/Rx Checksum") and also "Offload TCP_LargeSend" and "Flow Control" but no help. Still I have teh same problem: "250 Ok" is missing at the end of SMTP transaction with yahoo servers. After 10 sec, MercuryE quits.

    - I changed NIC to integrated "VIA Rhine II" but the problem still persists.

    - I installed Mercury server at another computer, part of the same local network and the problem is the same.

    - All computers in local network gets to the internet via Win2003 computer which serves as a gateway / software router to ADSL modem.

    - I decided to skip the gateway, connecting Mercury server directly to ADSL modem but the problem is the same.

    - I tried with another SMTP client (Outlook Express with smtp server address set to be - exactly the IP of a yahoo smtp server) and I have the same problem.

    Regarding MTU, here is my situation:

    - I used TCP optimizer to test and set my MTUs (I tested from the computer where MercuryE is running). It's MTU has not been set so I believe 1500 was assumed. During "Largest MTU" test, when pinging with 1453 bytes, I got "Request timeouts". Therefore largest MTU could not be determined because of packets lost. I tried pinging different web sites but the same result.

    - I connected the computer directly to ADSL modem and tried the same. The results were the same.

    - I have set this PC MTU to 1300 manually and tried the test. TCP optimizer successfully confirmed largest MTU to be 1300, with no packet lost.

    - I tried delivering the same 5MB message to yahoo (using PC MTU 1300), but the problem still persists!

    - I can't say what was the real MTU of my ADSL modem, but I overided it's default settings by MTU 1300. After that, I tried to confirm ADSL MTU 1300 with TCP optimizer, so I started "Largest MTU" test on computer which already had MTU 1500. Result: when pinging with 1312 bytes, I got "Request timeouts". (Therefore largest MTU could not be determined because of packets lost.) Remember, before changing ADSL MTU pings timeouted on 1453 bytes, now it is 1312 - therefore I could accept appearence of this timeouts as a confirmation that ADSL MTU is now 1300. But I would prefere that "..fragmented" response is received instead of "timeout", because TCP optimizer would be able to determine the largest possible MTU, right? I wander why my ADSL modem doesn't return "fragmented" response..

    You suggested also that I "might simply want to turn off the MTU Discovery operation". I have no idea where (PC or ADSL modem/router) and how to do that.


    Anyway, If 1MB email message is ALWAYS successfully delivered to Yahoo and 5MB isn't, I would not expect that MTU is a problem because MTU problem would cause trouble during delivery of both 1MB and 5MB messages, right? (All packets will have the same size if the message is larger then 2KB, so all of them will be fragmented - except maybe the last one..) Or I am wrong?

    Thanks for help!






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