I bet you use CCleaner. It has been messing with folks settings in Thunderbird for years and it usually appears on the forum as a complaint about the message pane reappearing.

But I take issue with you idea that viewing the message will tell the spammer anything. Unless you enable the remote images in the message.

I have been hearing from people now for decades really, sprouting the same basic information you are, about security and spammers knowing your email address is live. Lets look at this in a sane and reasoned manner.

What better way to determine if an address is valid than to send mail to it and not be notified by the receiving server that the mail is rejected because of there being "no account". What your view of email discounts is that the mail has already been delivered without apparent error to the server, to your mail box. That occurs without your involvement in any way.

Do spammers even care if the address is valid? The answer is almost assuredly not. Marketers like walmart amazon and ebay care, they care so much their emails are almost all tracking tools. Did you click a link? What link did you click? Did you read the mail more than once? Did you share the link? did you buy from the link? Spammer just send out millions of mails and hope some make it through the spam filters. It is not like the old days where you send it is gets delivered anymore. Spammers have bigger deliverability issues than wondering is an address is valid. We see folk hit by backscatter, because the spammers are so disinterested in the individual emails they send out they use fake or borrowed from and notifications to addresses.

How do spammers know you read the mail? Thunderbird does not allow scripts in email, so that common avenue of phoning home os simply not available. The only practical to phone home is to load remote images (ala walmart, ebay etc.). We turn off remote images by default for this sort of security reason.

Finally to use an old mail analogy. Getting an email and not opening it is analogous to getting a letter delivered by the postal service and not opening the envelope for fear of telling the sender you did. In both cases there is no connection between the sender and the recipient to allow that to happen.

Hi Matt, Thanks for the reply, I think?? Could you have been just a little bit more patronising? With a little bit more effort I am sure you would have been up for some sort of award. So close.......... ! I am sure also that you must be one of those people that doesn't use any sort of protection against spammers and and viruses or pups. I bet you had that warm, fuzzy feeling whilst forming your reply, ie. this'll show him!!! Help like yours I could do without. For all your posturing and putting me down and belittling me, you didn't provide any sort of answer to my question. I guess in your mind that doesn't matter, perhaps the fun you had, shooting me down was enough for you. If this is what passes as support from Mozilla I'll never use it again! I am sooooo glad I got this reply before volunteering for Mozilla Support as asked, but then judging by your opinion of me, Mozilla Support will thank you for that. They dodged a bullet there! Just feel the warmth :-)

  For the record I am the wrong side of 50 and my current system is, in part, shown below. I have been using computers since 1981 with the ZX81 and later with the Amiga 1000 (It was an early NTSC model so I had to change out the Agnes chip iirc and the onboard crystal to convert to PAL). I started using Windows in 2003. As an aside I was a VIP guest at the 1987 AmiExpo in New York.
  

Regards,

              Mark.

Phanteks Enthoo Primo case, Asus Crosshair Hero VI, AMD Ryzen 1700x, Gigabyte GTX970x2 Sli, 16Gb Corsair Dominator Platinum, Corsair 500MB boot drive with 3GB and 1GB HDDs, Bespoke watercooling loop incorporating Xspc Raystorm Pro, 13/10 PETG with Primochill revolver fittings and EKWB xres 3. I am in the process of changing my water pump to Laing DDC1T dual ddc in a Aquacomputer dual ddc top. And Yes I realise that having this doesn't mean I am a Guru but it has been built up over the last 14 years; a bit here and a bit there so I must have picked up some knowledge, if only by osmosis.

Matts info is useful and it is never possible to know how computer literate or your level of understand in opening emails and their content. Your comments suggested you were not fully understanding some elements. Do not be offended as no offense was intended, just use the info.

You have not provided additional info as mentioned by Matt.

Do you use a product like 'CCleaner' ? If yes, then you need make sure that all Thunderbird files and folders are excluded. The reason we ask is this, your preferences eg: Message Pane is closed, are stored in files which may be being cleaned by a product like CCLeaner and so Thunderbird ends up using the default. This may explain why certain preferences are lost, hence why we asked and would appreciate an answer in order to rule this out.

Remote content is by default not enabled. So if you open an email which contains remote content and the 'Remote Content' is disabled, you will not see images, instead they are replaced by a black outline box. Do you have 'Remote Content' auto disabled? If yes, then this is the safest mode. This means that opening the email is ok, but if you then enable remote content in that email and click on the links, info may be collected. So this required a specific action on your part; opening an email in itself is perfectly safe. There is no difference between opening an email in the Message Pane and opening an email in a tab.

On a related note...regarding junk/spam emails: have you set up and trained your Junk Controls to deal with junk emails? Have you set up your address books as whitelists? https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages

Hi Toad-Hall, Thank you for your reply. I do use Ccleaner and I thought. I had made sure to untick any relevant boxes but I think one remained that may have been causing trouble, perhaps when I upgraded from free to pro and rushed the set up. I do have remote images switched on as I find it more convenient for me. As far as Junk/spam mails is concerned I use BTYahoo (ex BT Broadband customer) as my email service provider. This has quite a good junk/spam filter built in. I also use Bitdefender TS and that occasionally picks thinks up. I still take umbrage at Matts remarks, regardless of the fact that he mentioned Ccleaner as a probable cause. Three words would have sufficed EG. Check Ccleaner settings. But no, he had to make a big issue out of it, trying to make me look like an idiot in the process. I can manage that myself, without his help. Thanks again.

 Regards, 
             Mark.

match69uk said

Hi Matt, Thanks for the reply, I think?? Could you have been just a little bit more patronising?

I am sorry you are offended by the truth about email. I feel I have a obligation to correct those that promote clearly incorrect perceptions of email use in Thunderbird. A a poorly farm labourer I just tell it like I see it. Perhaps you have the education to make the words polite. I do not.

You said "I believe this to be a security risk as has been said for years. I am set to view all emails in HTML and if I get hit with a spammer, it is a dead giveaway that it is a live email address." I corrected this grossly incorrect statement and you took offense. You will never even start to comprehend how sorry I am I took the time to reply to you at all.

Did I tell you your were using ccleaner? Yes I did, in the first sentence of my reply. Did I say it messes with Thunderbird settings? Again yes, I did in the second sentence. But you needed someone else to tell you that in a manner acceptable to you for you to act on it.

You have done your best to make me leave this forum, and to be honest you may succeed. I am tired. To many years of the same questions and the same old wives tales and folk who do not know insisting that they do.

Hi Matt, I am sorry if you took offence at me taking offence for the tone of your email. I assure you I was not 'promoting' anything, it is just my opinion, which by its very nature cannot be wrong. I do not think hackers or spammers are sat at their keyboards checking individual emails. I am sure that hacks have been written to check if a request is made to download any image info from the servers. This could then be added to a list of live emails that could be sold to whoever. Perhaps the situation has changed now, but my experience of this is based on the situation in the early 2000s. I will however accept that certain requests for support can leave one speechless, especially if the question has been asked a thousand times before, but that is the nature of support. One only has to look at feedback from say, android apps to see that some people think they have the right to Demand support with phrases such as "FIX NOW!!" or "If you do not fix this now I will uninstall your product!", and this is for free apps. I too have felt the urge to slam some of them down for reactions such as this; occasionally I have. I would hope that you don't stop offering support because of anything I said. In my defence you say you are poorly. I am disabled and have recently found out that I need major surgery if I wish to live longer than a few years (C). My mood at hearing this news may have been a reason for me replying how I did. Best Wishes and Regards,

              Mark.