E-mail being bounced

[#1]

I'm working on a job application document from home, having e-mailed it from work to my home account without difficulty.
Having updated it, I've just tried to send it (an .rtf file in Libre Office Writer) back to my work e-mail address. It has just been bounced as follows:
"An error occurred while sending mail. The mail server responded: dxD11m0034epeuC01XD2vA message rejected due to spam or virus.".
My workplace is a large government department, and I've never had any problems sending e-mails with attachments to my work account before.
The .rtf has been scanned by an up-to-date version of Avast! and is clean.
I tried logging into Webmail and sending it that way, and it seems to have gone through (although it'll be Wednesday morning before I can check to be sure).
Any ideas?

[#2]

Best thing to do will be to raise a support ticket with the following information:
Subject of the email:
Sender Address:
Recipient Address:
Error code:
Approx time /date of sending:
And if possible a copy of the email headers -> http://www.plus.net/support/email/email_troubleshooting/obtaining_headers.shtml
Hope this helps,
Cheers,
Matt

[#3]

Looks like the new version of Avast! was doing it. Once I disabled "Scan outbound mail (SMTP)", the problem went away.

[#4]

Does Avast add a footer to the email? Wondering if the problem was due to that (the error suggests that it's the content of the email that caused the spam filter to trigger).

[#5]

Odd...
Just re-enabled scanning of outbound SMTP and sent identical e-mails as before with no problem.