What is embarrassing about that? It is not optimal, but it does prove the filter is independent. :) Most marketing mail, and lets face it the thank you is more about marketing than anything else, skirts the definitions of spam. It is unsolicited, generally has embedded tracking data which I at least, see as an invasion of my privacy. Even if it is only a web beacon it is a tracker. Then we look to Thunderbird's junk mail controls which learn from you what you think is SPAM and in doing so has no regard for the email addresses used as they are really not a good indication of SPAM. So of course for some folk the learning filter will include mail from the donations address as spam. If I was not aware of Mozilla and Thunderbird's rather odd relationship with the Mozilla company and foundation, as well as the involvement of the MZLA corporation in the building of Thunderbird. I would question why an email is purporting to come from a mobile sub domain,with a reply to another address on the main domain. That looks SPAMMY to me. Personally I suggest you reply to the address given. It is legitimate, some years ago I used to reply to mail to that address. Ask why their email to you might be such that the Junk filter identifies it. It is an issue that those directly involved in the donation process should be aware of. Your point is in many ways quite valid, it is just it does not surprise me that this could occur.