|Sándor Zsolt||May 26, 2006 2:25 am|
|Daniel Faber||May 26, 2006 3:32 am|
|Sam Varshavchik||May 26, 2006 3:50 am|
|Sándor Zsolt||May 26, 2006 5:36 am|
|Gordon Messmer||May 26, 2006 9:52 am|
|Daniel Faber||May 26, 2006 10:33 am|
|Gordon Messmer||May 26, 2006 10:40 am|
|Arno||May 26, 2006 11:26 am|
|Daniel Faber||May 26, 2006 12:10 pm|
|Sándor Zsolt||May 29, 2006 2:51 am|
|Sam Varshavchik||May 29, 2006 6:16 am|
|Sándor Zsolt||May 30, 2006 12:26 am|
|Sam Varshavchik||May 30, 2006 3:55 am|
|Subject:||Re: [courier-users] Considerable time when "550 unknown user" error msg. at local domain|
|From:||Sándor Zsolt (sand...@mail.vpop.hu)|
|Date:||May 26, 2006 5:36:49 am|
Thanks for your answer. I didn't know it.
I see, this is a self protection method. It's okay - I think - if the server is directly on the Internet, but in our case it is behind a firewall what does a prefiltering and relays the good domained messages to the mail server. (The firewall can not check wheather the user in the domain exists or not it simply relays all of them.)
Problem is that our firewall could open only max 30 smtp connections at a time - it's a built in limit, cannot be increased. Just imagine 30 smtp connections with full of waiting badly addressed, or spam mails. It holds up not only the spams but painfully also the normal mail traffic. Of course the firewall cannot differ the good and bad mails, it needs to relay them to the mailserver what processes and rejects the bad ones. Yesterday we had 25 thousand badly addressed mails while the good ones were less than 10% of it with 3 hours average delay! This is not good. Had there be a quick smtp conversation between the firewall and the mail server it would have not been any headache.
The bottleneck in this subject is that the firewall and the mail server use their own self protect mechanisms, which in turn results the long delay of the good mail traffic. It seems that we could not increase the active smtp process numbers on the firewall (already contacted to the developers) so we try to cope with the issue. What do you think of it? Is it possible to suspend/decrease the delays in the smtp sessions in courier some way if the user is unknown? This could speed up message processing and in turn decrease the delay of good mails.
Thank you very much for your help and time.
On Friday 26 May 2006 12:33, Daniel Faber wrote:
On 26/05/06 11:25, Sándor Zsolt wrote:
The whole system works fine, but recently notified that the incoming mails - from the Internet - suffer considerable delay. Tracking the problem we found out that it is caused by the huge amount of spam mails, where the local domain is correct, but the addressee is wrong so courier gives back an:
550 User unknown
error message. This is all right, the only problem is that this response arrives after a considerable time. It takes at least 8 secs, but sometimes even 2 mins.
2 minutes and 8 seconds?
Look at this SMTP dialog:
$ telnet helium.leptonite.de smtp Trying 22.214.171.124... Connected to helium.leptonite.de. Escape character is '^]'. 220 helium.leptonite.de ESMTP HELO its.me 250 helium.leptonite.de Ok. MAIL FROM: <ma...@daniel-faber.de> 250 Ok. RCPT TO: <noth...@leptonite.de> --- delay: 8 seconds --- 550 User unknown. RCPT TO: <noth...@leptonite.de> --- delay: 16 seconds --- 550 User unknown. RCPT TO: <noth...@leptonite.de> --- delay: 32 seconds --- 550 User unknown. RCPT TO: <noth...@leptonite.de> --- delay: 64 seconds --- 550 User unknown. RCPT TO: <noth...@leptonite.de> --- delay: 128 seconds --- 550 User unknown.
My guess: it's not a bug, it's a feature to slow down spammers.