Previous replies to this problem have suggested it is a matter of the recipients' spam filters. Well, my emails are not spam, they have no links or other complicating factors, they are simple words making up an email. Many recipients receive my emails fine; one person receives them with a big banner across the top, warning this may be spam; my city government has apparently a very sophisticated spam fllter (not surprisingly) and it simply blocks all my emails. I learned this by trial and error when city staff were not receivng my emails. So I send emails to the city directly from my ISP, bell.net in Canada, instead of from Tbird. This means I do not have a complete set of sent emails in the Thunderbird file. And for the other emails I send, I can't tell if they are received or are blocked as I get no message back saying the email was blocked. Other recipients than the city may be blocking my emails erroneously as spam and I don't know that. As I say, my emails are NOT spam and there should be no filter that would treat them as such. Is there something in Thunderbird contributing to this, or can I change settings of some sort? Does it have to do with how bell.net processes my email before it sends it on? I have NO problem with incoming mail, so changing the incoming spam filter will not address this problem - duh. Thank you for any help.