How do you know that you are sending these spam emails?
My own address is in my address book they are always from
[email protected]
Are you receiving undeliverable message emails?
Yes, usually from known bad addresses that have not been deleted, that's how I know it's an old address book, some of them are from companies that ceased trading six years ago, long before I started using Thunderbird.
Are these random addresses from your address book? Or just random email addresses?
They are seemingly random addresses from my book. My address book is not vast say 150 entries and the mails usually go to about 40, some of which bounce. Some are getting through.