Missing messages or delayed reception from some domains with larger e-mails? RSS

1

Environment is Exchange 2010 latest SP/rollup on SBS2011 with latest SP/rollups (2008R2 functional)
Watchguard x550e Firewall latest version 11.3.5.
ORF latest version 4.4.

This one has been bugging me for months. I've asked on Watchguard and Exchange forums, and no response. Figured I'd ask here:

Basically we have two companies that when/if they e-mail us we don't get all their mail, or it is delayed. I've whitelisted both domains and related IP addresses in ORF.

I've tried changing our firewall rules to not do any proxy or filtering, basically accept all messages. Hasn't made a difference.

I've tried changing Exchange for SMTP receive logging, but when I look at the logs I don't even see all the messages that are sent us. Not quite sure why some messages show up in the protocol logs and some don't.

Below is a sample ORF log screenshot filtering one user from this domain to one of our users. As you can see, look at all the whitelisting, but nothing else. User received mail only where subject line showed:
http://i.imgur.com/6m5MJ.png

On both domains they put in a packet inspection and said that we are "throttling" connection attempts, and messages are then timing out, especially larger messages with attachments. I don't know where in Exchange this "throttling" would be occurring. Exchange should be passing it or rejecting it based on SCL, I would think.

We receive thousands of e-mails a day of up to 40 megs without issue from hundreds of domains. Only two domains we have this issue with.

Ideas?

by Indy 6 years ago
2

@Indy: AFAIK throttling of an SMTP connection is not triggered by SCL thresholds: it depends on the message size, number of recipients, and the frequency of transmissions. I assume the large message size makes Exchange tar pitting the SMTP connection, which eventually times out (the sender gives up). See these articles:

http://technet.microsoft.com/en-us/library/bb232205.aspx

http://technet.microsoft.com/en-us/library/bb201658.aspx

by Krisztian Fekete (Vamsoft) 6 years ago
(in reply to this post)

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