Why does Exchange block GPG-encrypted messages?

I am trying to implement an encryption solution using GPG, but it seems our Exchange server is blocking every message that has been encrypted. Signed messages work fine, and receiving encrypted messages also works, but as soon as i try to send an encrypted message, i get a mail from "System administrator" (wouldn't that be me? ;)) telling me that the the message couldn't be delivered, and a pretty uninformative error-code: [0x80004005-00000000-00000000]. Googling it doesn't really turn up much. I have tried disabling our av/spam detection and smtp scanner in our sonicwall, but to no avail. We also have a trend-micro mail scanner running on the exchange server, which i've also tried disabling, and it doesn't help. I've also tried checking and fixing the exchange servers mailbox store integrity, no help either. Can anyone help?
markqvistAsked:
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markqvistConnect With a Mentor Author Commented:
Turns out theres a bug in gnupg that prevents it from sending through exchange. I solved it by installing a local smtp server on the computers and sending through that :)
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MesthaCommented:
I doubt if it is Exchange blocking the message. The AV would be my guess. Unfortunately disabling the AV is not enough, you need to remove it. When it is disabled its hooks remain in the system.
It could also be your firewall, if that scans SMTP traffic.
Exchange doesn't care what the message is, but something scanning the traffic would.

Simon.
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markqvistAuthor Commented:
Thank you for the feedback. Unfortunately, totally removing the AV is not an option, since it is running on our production Exchange server, and it also wouldn't be very smart cost-wise, since we already paid for a license that runs a few years from now. Can you suggest alternative options? We are running Trend Micro as our antivirus.
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markqvistAuthor Commented:
To clarify, I didn't just disable the AV entirely. I went to the configuration console and disabled all scanning modules relevant for outgoing mail traffic.
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MesthaCommented:
Due to the way that the AV integrates with Exchange, removing it is the only way to prove it is not the cause of the problem. Disabling it is not enough, because of the hooks in to the application.

You need to remove it, then reboot. If the problem goes away, try reinstalling it. If the problem returns then you have to go back to Trend and ask them why they are blocking the messages.
If they cannot assist, then you will have to find another product or use a different system to encrypt messages.

Simon.
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markqvistAuthor Commented:
Thank you for your insight. I guess I will just have to try it out... We'll see if it works ;)
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