On a number of occasions we have been informed by a few different clients that emails from particular (but varied) senders are being received multiple times - like 100's!

Looking at the logs our end, we don't see a problem - to us we just see the sending server make a connection, send an email which we forward onto the destination server. I've now been able to get hold of some sort of log file from one of the senders which are experiencing this 'duplication' of emails. From what I can gather, there system connects and sends SF the email, SF does whatever checks it does, but before SF accepts/confirms delivery, the senders end hits a time out, drops the connection and re-queues the email for another delivery attempt later. Despite the senders end timing out before our server has confirmed receipt or acceptance, our server still forwards the email - presumably because our server knows its received the email in its entirety having receiving the <CR>.<CR> instruction? So assuming the email passed spam checks, the email is sent on. 

The above course of events cause a loop, whereby our server receives and delivers the email, the senders continually times out before our server has confirmed acceptance, causing the sending server to re-queue, and re-deliver the email - and then the loop begins again.

If this is what's happening, I think either one of the following is wrong:

1) The senders end's time out is too short?

2) SF should not deliver an email if the connection is dropped/times out - just like it wouldn't if the connection was dropped part way through the DATA stage.

If number 2 is changed, so that SF does not deliver emails from which the connection is dropped even after a <CR>.<CR> is received, this will not prevent the senders end from timing out, so instead of receiving duplicates, our server would not forward any, meaning the email would never be received, and eventually a bounce back would be generated. What are your thoughts on this? And what do people thing the fix might be? 

 

Do you find solution on this?

 

Thank  

 

IdleDisconnectMinutesTimeout=240
ReadTimeout=300

ReadTimeoutOutgoing=60

 

The max email size is disable

 

And I don't think it's the firewall because I received te email and attachment.

 

I'm actually in a email loop, so I can trap next network communication and send it to you?