Thunderbird has a rather simplistic scam detection system. If it sees links to "other" sites in an email message it reports it as a possible scam. This affects many legitimate mails that quite reasonably offer links to other sites. Unfortunately, your options are to suffer as it is, or switch off the scam detection altogether. There are no settings to teach it or to set safe sites. :-( Unlike spam detection, it pays no attention to the ''from:'' address. If the sender is in your Address Book, they should never be identified as spam. My personal bugbear are those messages that come from magazines and the like, with a unique and apparently randomized ''from:'' address each time. You can't add these to Thunderbird's Address Book to effectively whitelist them. I hear rumours that the Address Book is being revamped and hopefully both the scam identification and the possibility to whitelist by domain will be included as part of the improvements.