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We have an exchange server, and are having problems when sending email to three of our customers.

When there are no attachments the email is delivered successfully, when a pdf (from a word doc) is attached, size around 1mb, the email is delivered successfully, but when the attachment is a pdf from an autocad drawing, size only 500kb the email fails and nobody gets an NDR.

Background info:

The problem started around 2 weeks ago, all fine before that. I was recently asked by our ISP to turn off NDRs due to backscatter. We are sending through smtp.blueyomder.co.uk, I wondered about antispam filter/blacklist issues? I can successfully send an email with a 9.5mb zip file containing pdfs to a gmail account and a yahoo account.



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You shall not disable NDRs. Otherwise you wonder yourself why you don't get NDRs. –  mailq Oct 11 '11 at 13:52
So what is your question here? The sentence with the only question mark in it is not a question. –  mailq Oct 11 '11 at 13:53
The question is why/how does email fail, depending on which program created the pdfs in the attachment? and I will turn NDRs back on to see if any clues there. –  ajp Oct 11 '11 at 13:59
Also look into the log files and present the rejection or delivery confirmation of the mail(s). Then present the relevant log entries. –  mailq Oct 11 '11 at 14:09
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