I think this is the recipient's problem, rather than yours. Their spam detection is causing the trouble.

However - was that "spam" or "junk"? If it were "junk", can we infer that the recipient is a Thunderbird user?

Thanks for your response. I believe my emails are being filtered as both spam and junk. The recipients are both Thunderbird users and non-Thunderbird users.

"Junk" shouldn't really be a problem. Thinking about correspondents who use Thunderbird, if your address is in their address books it shouldn't be able to set your messages as Junk. It could probably still decide your messages are scams, since that is an separate mechanism and is triggered by multiple links to assorted websites and domains.

Spam detection is generally under the control of the end user. Your recipients should be able to get you whtelisted.

Can I ask what is the nature of your messages? Do they contain links to other sites or material that might be thought to be commercial in nature?

I have both a Thunderbird and an MSN email account. I forwarded an email from my Thunderbird to my MSN and it ended up in my Junk folder. I've forwarded emails to myself in the past without any problem. This particular email did not contain any links, files or images. However, there are times when my emails do contain links to another site.

I understand I can correct this by white listing my Thunderbird email in my MSN email. However, my concern is that emails I'm sending from Thunderbird to other recipients are also ending up in their junk and spam folders and they are not receiving my communication.