Exchange Message size limit

We have Exchange 2000 Server SP3. When ANYONE external to our organisation tries to send a message with an attachment that is 5MB or larger, the message does not get delivered through because of the message size.  If we send a file internally of 5MB+ everything is fine.  We have set a "Receiving Message Size" limit of 50000Kb.

I have checked message sizes from MS Knowledgebase article 322679 but it still doesn't work, any ideas?
p_tippettAsked:
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David WilhoitSenior Consultant, ExchangeCommented:
That article lists all the limits there are. Either you're missing a piece, or you need to restart the server to ensure the settings took effect. But there's no other hidden piece. Is this the only E2K server? Is there a gateway SMTP server that Exchange forwards the message to, before it leaves your org?

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RobmonsterCommented:
Are you sure the bounce is being generated by your Exchange server? Many ISP's place limits on the size of emails that pass through their systems. Its a possibilty that the mail is being rejected by your ISP before it gets anywhere near yoiur own server. The fact that sending an internal mail works perfectly fine would point to this,.

As a test, set the Receive limit on one mailbox and try sending the same file internally to that mailbox. If it then gets rejected then you know that the problem must be somewhere with your upstream provider.

RM
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p_tippettAuthor Commented:
Yes, we run Mailsweeper relay software which is passing onto the Exchange server.  The error message generated according to the mail header is from our Exchange server.

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David WilhoitSenior Consultant, ExchangeCommented:
do you have the send size and receive size both set, or just one of them?

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p_tippettAuthor Commented:
We have a send size set at 10000 and a receive set at 50000.  

Bear in mind these settings haven't changed in two years and the server has been rebooted on many occasions.  

It almost seems like a ghost limit exists somewhere but cannot be changed through a user interface.
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David WilhoitSenior Consultant, ExchangeCommented:
Saw this, figured you have to but thought I'd post it anyway.

This problem occurs because of the method that the Exchange message categorizer uses to enforce message size limits. The categorizer does not differentiate between incoming messages and outbound messages, and it applies both message size limits to all messages. For example, the categorizer uses the following logic when the categorizer determines whether to deliver a message. The message is delivered if both the following conditions are true: • The size of the message that is being sent is less than the limit that is configured for the Sending message size option.

-and-
• The size of the message that is being sent is less than the limit that is configured for the Receiving message size option.  
Note The message size limit that is configured in the Sending message size option limits the size of messages that can be sent. The message size limit that is configured in the Receiving message size option limits the size of messages that can be received. These message size limits are applied to the whole organization. These sending and receiving message size limits also affect messages that are sent to and that are received from recipients who are not members of the Exchange organization. These global settings affect all Exchange recipients. If a recipient has configured their own personal sending or receiving message size limits, the global message size limits override the individual message size limits of the mailbox.

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p_tippettAuthor Commented:
Done some digging around,  if I send a 5mb / 6mb attachment - all OK, if I send anything over then Exchange refuses and I get an NDR.
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RobmonsterCommented:
Although the receive limit you have set should be fine, have you tried increasing it (say Double..) to se if it makes a difference?
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p_tippettAuthor Commented:
Trying that now!!!  Any other ideas in the meantime?
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p_tippettAuthor Commented:
Amending the "Send Limit value" appears to resolve the issue.  We can now accept mail attachments over 8MB upto our new limit.
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David WilhoitSenior Consultant, ExchangeCommented:
It's all about the categorizer....smallest message size is most restrictive limit.

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Javier RodriguezOwnerCommented:
I have a similar problem and the reason is that the server takes into account the data included in the email header.  

For example:

We have send/receive limits of 25 MB in our Exchange organization, but the true limit is 18 to 19 MB.  I cannot remember where I got this info, but we verified to be correct.  If i was you, i willl do a proportion to determine what is the "true" limit in for your organization based on the numbers that I provided.

Hope it helps!

JR
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