SMTP Failure with Large Attachments

[Guest]

Hi,

I have created a website using C# ASP.NET 2.0. Users of the website are
able to generate reports and email them from the website using SMTP mail
configured under IIS 6.0.

Although this works most of the time, messages greater than 2MB are bouncing
when being sent to one domain (A). However, I can send much large files from
the website (W) to my own address (B) and my hotmail account (H). I can then
forward these emails to (A) without any problems.

The failure messages are:

Status: 5.2.3
Diagnostic-Code: smtp;450 5.2.3 Msg Size greater than allowed by Remote Host


In summary,

W to A fails
W to B OK
W to H OK
H to A OK
B to A OK

The website's hosting company are saying that there are no restrictions on
outgoing mail sizes. A's company have a size limit for incoming files, that
is far higher than the 4MB messages that fail (by a factor of 10).

I am now at a loss on how to diagnose this problem, so I'm looking for any
help you can give.

Regards,
Dave.

 

[Walter Wang [MSFT]]

Hi Dave,

Is it possible that there's some spam filtering software on A will use
different message size limit according to different sender? Apparently
you're using different sender when sending from W, H or B.

Sincerely,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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[Guest]

No, apparently the spam filter still lets through 38MB files.

 

[Walter Wang [MSFT]]

If you use other email client to send email from domain W to domain A, does
this issue also occur?

You may also try to compare the MIME header in the email that failed to
send from W to A, with the email that is successfully sent to A from B or H.

Regards,
Walter Wang ([email protected], remove 'online.')
Microsoft Online Community Support

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[Guest]

We have now carried out a large number of tests and now believe that the
problem is with the recipients server. We just need to convince them that it
is their end.

Since there is nothing wrong with our ASP.NET code, this question can be
closed. Thank you for your help.