Given Thunderbird respects the addition of the person to the address book, I would suggest you issie is spam filtering server side. One of the wonders of IMAP is you get to work out which is messing in your cage. Most often it is server software because mail providers utilize some fairly bizarre rules. rejecting .eu domains sounds exactly like something I would expect from a xenophobic US based server administrator. They can not imaging why anyone using a .RU or .EU domain would legitimately send mail to them

Thanks for the input, Matt. This was my thought too, at first, so my first foray into solving this problem was on the support forum for the server. I'm using SME Server 9.2 - a very decent canned SOHO package with a long pedigree that I've been using with little trouble for several years. The experts could find nothing in the logs I posted to indicate that the server found anything objectionable. At the client (TB) end, it positively refuses to accept that the mail isn't spam, which is odd: as the human - the adult in the room - it should be my privilege to mark something as not spam if I so choose, but I it will not let me do so. When I un-check an email item that has been so marked and moved to the spam folder, TB takes it out, put it somewhere, then re-marks it as spam (sometimes) and within a couple of seconds puts it right back in the spam folder again. It won't learn that that sender is legit. I thought that that is what learning is all about.

The only use in Thunderbird spam filtering for the address is in the whitelist function. The actual address is not in any way used in the Spam filter itself.

As you appear to me using Windows you probably have an internet security suite and also probably it contains some sort of phishing and spam filtering. They just can;t help themselves those anti virus comanies. They have to make a swiss army knife of tools that are functional but seriously a poor choice. But it looks good on the packaging. Perhaps take a look there. (Note that recent experience indicates that some anti virus products inject their DLL'd into the running Thunderbird process, so checking places like add-on, while a good idea, does not exclude anti virus interference.)

You might also want to look at the RBL lists used to do the server side spam filtering. Spamhaus in particular as they tend to block a lot of "consumer" IP addresses so home server fare really badly. See http://distro.ibiblio.org/smeserver/contribs/rmitchell/smeserver/howto/Spam%20blocking%20HOWTO%20using%20qpsmtpd%20&%20RBL%20for%20sme%20server.htm

Thanks, Matt. It may amuse to to know that your reply which came into my mailbox was also marked as spam :-) You've added a third area of focus, though, and I'll investigate as you suggest.

julianop said

Thanks, Matt. It may amuse to to know that your reply which came into my mailbox was also marked as spam :-) You've added a third area of focus, though, and I'll investigate as you suggest.

That in itself maybe a clue. These forum emails originate in Amazon AWS. Quite probably also a known SPAM source as are shared servers in "cheap hosting" solutions and servers located on "consumer" IP addresses.

Good to know. In the time between your emails, I had turned off spam filtering in TB, and your latest email came through without interruption. What would you suggest I do now, given this development?

Oh wait... I'd also turned off Ad-Aware filtering... I'd better separate these factors, hadn't I? I leave TB off, and reenable Ad Aware...

And I suppose I reply again so you have something to filter.

Thanks for doing so :-) So, with AdAware still running, but adaptive junk mail filtering turned off in Thunderbird, your email was not filtered. I'm going to reverse the factors now: turn off AdAware and turn on adaptive filtering. Would you be kind enough to ping me again?

julianop said

Thanks for doing so :-) So, with AdAware still running, but adaptive junk mail filtering turned off in Thunderbird, your email was not filtered. I'm going to reverse the factors now: turn off AdAware and turn on adaptive filtering. Would you be kind enough to ping me again?

Done

Thanks again. But now that's interesting: your email wasn't rejected this time. That's probably because it learned from the last time, and "remembered" the training from my first correction, before I disabled training. Well, OK, that means that junk training works. Now I have to wait to see what happens when I get emails from European TLDs, like .eu, .br and .dk, which have been rejected recently. As I remember, it's still only the one .eu bloke I get email from whose emails won't train to be not junk, but that might simply be low sampling. Thanks again for your help, Matt. I have more experimentation and data gathering to do now, so I'll let this thread go quiet until I either find something conclusive, or have more need of help.