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out of sequence smtp communication

2005-04-25 05:29:35


I have a problem with smtp transaction.
I often get a 503 error, well far more often than i would like.

The destination mail server accuses mine of sending a MAIL FROM before
it has received the EHLO/HELO command, duplicate EHLO/HELO or of out "out of 
sequence smtp communication"

I have attached an example packet sniff at the bottom. If someone wants the
full sniff I can send it off list, its about 22k for this example.

The server is exim 4.32 (RHEL3) but this occurs using pmdf7(vms7.2) as well and 
the remote mailservers
are all types from exim,postfix,qmail,sendmail, mailmarshal, exchange and some 
i have not heard

A couple of odd things:
1. I get retransmissions in under 1 sec ( faulty misconfigured router ? ). 
There are 2
cisco routers between the mail server and the outside.
2. the retransmission of the 250 response appears in numerous place and not 
only the 503 error
however all the 503 errors do have a retransmission error of their 250.
3. This is all on top of tcp, while my tcp is abit rusty i thought tcp 
guaranteed a connection and
handled errors for things running on top of it, barring long timeouts of 
course, yet i seem to loose commands for some reason.
4. It is not specific to a particular server and 10 seconds later sometimes 
another mail will go through to the remote server,
without the error.

Any suggestions would be greatly appreciated.


No.     Time        Source                Destination           Protocol Info
     99 6658.472911        TCP      51897 
> smtp [SYN] Seq=0 Ack=0 Win=5840 Len=0 MSS=1460
SV=514476065 TSER=0 WS=0
    100 6658.802093         TCP      smtp > 
51897 [SYN, ACK] Seq=0 Ack=1 Win=24616 Len=0
TSV=1960788066 TSER=514476065 WS=0 MSS=1460
    101 6658.802114        TCP      51897 
> smtp [ACK] Seq=1 Ack=1 Win=5840 Len=0 TSV=514476098
    102 6662.990160         SMTP     
Response: 220 ESMTP Thu, 21
Apr 2005 10:13:55 +0200 (GMT)
    103 6662.990198        TCP      51897 
> smtp [ACK] Seq=1 Ack=79 Win=5840 Len=0
TSV=514476517 TSER=1960788486
    104 6662.990311        SMTP     
Command: EHLO
    105 6663.979447        SMTP     [TCP 
Retransmission] Command: EHLO
    106 6664.274916         TCP      [TCP 
Previous segment lost] smtp > 51897 [ACK] Seq=93
Ack=27 Win=24616 Len=0 TSV=1960788616 TSER=514476517
    107 6667.190539         SMTP     [TCP 
Retransmission] Response: 250 2.0.0 OK
    108 6667.190648        SMTP     Command: 
MAIL FROM:<nolank(_at_)tlabs(_dot_)ac(_dot_)za>
    109 6667.423687         SMTP     
Response: 503 5.0.0 Polite people say HELO first
    110 6667.423822        SMTP     
Command: QUIT
    111 6667.423850        TCP      51897 
> smtp [FIN, ACK] Seq=65 Ack=133 Win=5840 Len=0
TSV=514476960 TSER=1960788939
    112 6667.659639         SMTP     
Response: 221 2.0.0 closing
    113 6667.659704        TCP      [TCP 
Keep-Alive] 51897 > smtp [RST] Seq=65 Ack=1936846515
Win=0 Len=0
    114 6667.676195         TCP      smtp > 
51897 [FIN, ACK] Seq=192 Ack=65 Win=24616 Len=0
TSV=1960788962 TSER=514476960
    115 6667.676217        TCP      [TCP 
Keep-Alive] 51897 > smtp [RST] Seq=65 Ack=1936846515
Win=0 Len=0
    116 6667.676781         TCP      smtp > 
51897 [ACK] Seq=193 Ack=66 Win=24616 Len=0
TSV=1960788962 TSER=514476960
    117 6667.676786        TCP      51897 
> smtp [RST] Seq=66 Ack=1936846515 Win=0 Len=0

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