The junk white list and address book are no longer linked as they were, but the most common cause of complaints these days are Yahoo account holders as Yahoo forces their list on you. No whitelisting allowed.

Not a yahoo account, opera mail (under windows) does not do it,

Well what mail provider? Is the account IMAP or POP?

Your operating system is reported as Linux by the forum. What is the relevance of something in another application on another operating system to the diagnostics?

It is a Imap account hosted by Pickaweb and I currently use both os's on my computer both with thunderbird. The opera reference shows that is is not something the isp is doing, it is solely a thunderbird issue. I use thunderbird as it is cross platform