问题描述：
英语翻译
We had problem with our antispam system this morning (CET) and thats why your email to me bounced.
Did you get my email about the TCP window size issue?Any ideas about the reason?It must mean that your email server is so busy so the TCP/IP stack cant receive any more packets and sends TCP win=0 to packets the sending server so the SMTP session idle until your server can receive packets again.I dont know yet if it is our outbound SMTP server,our firewall or your equipment that after a while terminate the session but I will continue to go through logs etc to try to find the reason.
In my packet traces (I use Observer Suit from Network Instruments) I do see that the 1st mail with a PDF of 20 kB went through without any problems and no TCP Win=0 packets from your server.The second mail with the 250kB PDF first timed out after your server sent alot of TCP Win=0 packets,and then later our server resends the same mail again and this time it is sent without problem and without any TCP Win=0 packets from your server.
For the 3rd and 5th mail I never see that the mail are successfully sent.I only see that the SMTP sessions starts and then the sessions idles when your mailserver send TCP Win=0 packets...
The 4th mail with the PDF of 12 MB bounced back imidiatly due to your SIZE limit of 10 MB.
The 5th mail with a PDF of 7 MB timed out,and I got an SMTP error back after several hours.
I've sent 5 mails to you but only received 2 reply's from you.The only normal error message I got was when I tried to send a PDF with a size over 10 MB.The others seems to have been sent.
I do see some strange behaviour from your server but dont know yet if this cause the problems.
For several of the mails I sent (and also others I've seen) your server sends a huge amount of TCP ACK's with Window size=0 which means that our server stop sending more data,and wait until it gets a ACK packets with Win size greater than 0.I can see several ongoing SMTP sessions were the only packets that are sent is ACK's with Win=0 from your server,and if this maintains a long time it might occour that the SMTP session times out.
Our firewall is set to drop SMTP sessions that haven't sent any packets at all during 10 minutes,so I dont think this is the reason as the servers still sends ACK packets to each other.I have change this to 20 min anyway,to test to see if there is any change.I'll continue to watch my logs etc,to see if I find any other clues.
We had problem with our antispam system this morning (CET) and thats why your email to me bounced.
Did you get my email about the TCP window size issue?Any ideas about the reason?It must mean that your email server is so busy so the TCP/IP stack cant receive any more packets and sends TCP win=0 to packets the sending server so the SMTP session idle until your server can receive packets again.I dont know yet if it is our outbound SMTP server,our firewall or your equipment that after a while terminate the session but I will continue to go through logs etc to try to find the reason.
In my packet traces (I use Observer Suit from Network Instruments) I do see that the 1st mail with a PDF of 20 kB went through without any problems and no TCP Win=0 packets from your server.The second mail with the 250kB PDF first timed out after your server sent alot of TCP Win=0 packets,and then later our server resends the same mail again and this time it is sent without problem and without any TCP Win=0 packets from your server.
For the 3rd and 5th mail I never see that the mail are successfully sent.I only see that the SMTP sessions starts and then the sessions idles when your mailserver send TCP Win=0 packets...
The 4th mail with the PDF of 12 MB bounced back imidiatly due to your SIZE limit of 10 MB.
The 5th mail with a PDF of 7 MB timed out,and I got an SMTP error back after several hours.
I've sent 5 mails to you but only received 2 reply's from you.The only normal error message I got was when I tried to send a PDF with a size over 10 MB.The others seems to have been sent.
I do see some strange behaviour from your server but dont know yet if this cause the problems.
For several of the mails I sent (and also others I've seen) your server sends a huge amount of TCP ACK's with Window size=0 which means that our server stop sending more data,and wait until it gets a ACK packets with Win size greater than 0.I can see several ongoing SMTP sessions were the only packets that are sent is ACK's with Win=0 from your server,and if this maintains a long time it might occour that the SMTP session times out.
Our firewall is set to drop SMTP sessions that haven't sent any packets at all during 10 minutes,so I dont think this is the reason as the servers still sends ACK packets to each other.I have change this to 20 min anyway,to test to see if there is any change.I'll continue to watch my logs etc,to see if I find any other clues.
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