Confused send email error - size or virus issue?

[#1]

One of my referrals [coloured-headwear] is having difficulty sending an email....

This message could not be sent because its size exceeded the server's limit. You can use the option, located in Tools | Accounts | Properties | Advanced, to break messages into smaller parts.

Subject 'Re: New Lease for Nectars'
Server Error: 552
Server Response: 552 3Ln31w0043n9ACc01Ln7lp message rejected due to spam or virus. If you believe this is in error please login to your portal or contact your ISP support team.
Server: 'relay.plus.net'
Windows Live Mail Error ID: 0x800CCC6D
Protocol: SMTP
Port: 587
Secure(SSL): No

Time was around 09:45 today - the email size was just 13KB.

Removed parts [embedded images - hyperlinks] of the replied to email trail but made no difference.  In the end ripping out the whole of the replied to email trail allowed the email to be sent.

Any chance of...

1. Someone looking at the email logs to understand why this was trapped
2. Having the rejection reason clarified in the error report sent out - it is either a size issue or a virus issue not both!

Thanks.

[#2]

I don't think this problem will be anything to do with the message size, that will be just one of the meanings of the error code.

Based on your comments my guess is that the message contains a URL (possibly in its headers) that the anti spam appliances regard as suspicious. I think a staff member will need to see the email with headers to identify what triggers the report and reset its reputation.

[#3]

Yep, the size inference will be the client's (Outlook?) interpretation of the SMTP error. The cause will be the content of the reply chain, and something therein that's triggering our outbound spam filter.

[#4]

@bobpullen,

Thanks - email client is Windows Live Mail 2007 (IIRC).

Irony is that the inbound email did not fall foul of the spam filters.

Just how does one find the email headers on an outbound email which is trapped on submission... surely the headers are not there at all on the senders side ... until a successful submission?

[#5]

You don't. You'd need to share the source of the email you're referral was trying to send. Either that, or work out which bit of it is falling foul of the filters (it's normally a URL or image signature).

[#6]

... I did rip all of those out before I ruled out the whole of the original email from the reply.

Will see if I can reproduce it.