Outlook is blocking some of my emails, and I'm getting:

552 sid:M20A1i00E2qfw2F01:Message rejected for spam or virus content

EDIT: This has happened in Windows XP, with Outlook 2010 and AVG antivirus,

as well as Windows 7 (fresh install), Outlook 2010, and no antivirus (yet).

No matter if attachments are in email or not; It looks like sometimes if I try to re-send same message, but change the subject slightly (sometimes just adding a space) - it will go through.

The error I'm getting is instant, in my inbox, making me think it does not reach the ISP or SMTP server. Must be something internal, in Outlook. Any settings I can change to avoid this?

Please help...

I didn't find the right solution from the Internet.

References
https://social.technet.microsoft.com/For...t?forum=outlook

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