I have started to use Avast Pro with Outlook 2003 and I send all emails in plain text. I find sometimes that as I have ‘Insert Notes to Clean Uninfected Messages’ ticked that messages appear to convert to HTML. I know the easy answer is to turn this off but why is it doing it ? I am not sure if it is an error on my part in Outlook or a bug with Avast. It happens mainly on emails with attachments.
Any ideas ?
Regards
Gordonw
Maybe the attachments ‘transform’ your txt email into a html one.
Maybe you have any signature with pictures or something like that.
Just guessing…
Welcome to the forums, gordonw. 
Since I have used web email for years and have never used Outlook nor OE, I can not be sure if this has anything to do with your problem or not. But, Tech or someone else familiar with Outlook will say if so or not.
Anyway, maybe the settings in the picture below could have a bearing on your problem.
Thanks for the suggestions. I don’t use signatures and was advised when I spoke to tech support to turn off internet mail as I use Outlook as this may be conflicting.
regards
gordonw