I think outlook.com is broken.

http://downdetector.com/status/outlook/map/

How can it be down and allow me to log in through IE (with the same password)?

I like to think of email as an abstract construct. You could ask for an email account and be given an email address, along with a password and even the connection details.

However, the account that this login data represents may not yet exist. Someone somewhere has to activate this email account and associate your login particulars with it, and allocate some space on at least one server to handle your messages.

Even then, like the tree that falls in the forest and there's no-one there to hear it (so does it make a sound?) the account is virtual up to the point you start using it.

Now if we move forwards to assume that this account actually exists, then we can make use of it in different ways:

1. You might use a web browser, in which case you'll access it via the http or https protocol and a webserver. The webserver is a piece of software.
2. If you use an email client, that access will be through two or more email servers, using POP and/or IMAP, and SMTP. These are the standard protocols used in traditional email. (Practically, these servers are software and may actually all run on the same hardware. But I digress.)
3. If you use an "app" on your phone or tablet, it is likely that you'll be using yet another set of servers (software again) and protocols.

All three methods will at some point share the same set of data, but present it as existing in different interfaces, and maybe even in different mailboxes. An IMAP server may separate out Spam into its own folder, whereas a POP server might just post it to your Inbox, suitably labelled. So we have, in this situation, two different Inboxes.

Either or both of 2 and 3 could be in trouble, yet 1 still works. Different servers, different protocols, different interfaces.

This is all too philosophical, scientific or abstract for my apparently limited grasp on the inner workings of e-mail.

So, I have had a bunch of accounts, Hotmail and gmail, for a long time. They have all been set up in TB, also some time ago. They have all been working fine until a couple of days ago, when only 1 Hotmail account started acting up, asking for a new password when trying to access it via TB. Entering the -anyway correct- password changes nothing. Like I said, directly from IE, it works fine.

Settings within TB and Hotmail are identical to other accounts that are working fine both from TB and IE.

Because different programs or computers are involved when you connect via a browser (HTTP) as opposed to via email (POP/IMAP/SMTP).

The map at my earlier link shows outlook users all over the world having trouble. This is not specific to Thunderbird.

OK, so if it is a question of outlook having changed sthng in the way it accepts (or denies) logging in via e-mail clients in general or specifically TB, how come the remaining 6 or 7 Hotmail accounts work OK?

In my case it is the same computer, same IP, same time (as practical as possible, i.e. within a few seconds), so that leaves only TB vs IE. What is your suggestion? That I just wait it out indefinitely?

My point is that it cannot be as abstract and vague as you present it, almost as if it is internet spirits that deal with this and we are at the mercy of how their wives got up in the morning.

It is sthng specific and tangible that is causing this and it needs to be diagnosed and addressed possible at both ends (MS and Mozilla).

But it can, not all Hotmail or whatever email provider accounts are / will be affected by such an outage as in the maps above. Also, have you considering changing that accounts refresh timing? It is still very possible that you have exceeded the allowed locally or at the end point some request limiting threshold, which could exhibit many of the frustrating behaviors mentioned. Have you even bothered contacting Hotmail support?

Corey 'linuxmodder' Sheldon said

Hotmail support

At least we have humor here...

Hotmail "support", says that if I can log in via IE, it is TB that is screwing up... So, yeah, I have bothered with them. They haven't bothered with me though.

As to refresh timing, which is the first piece of solid advice as to what to do or check I have received and I thank you for it, besides general information, and assuming you are referring to the frequency of checking for e-mails that I have set up TB with, no, I have not tried changing it. However, it is the same for all accounts, so my guess is that if it would cause outlook to react, it should have done so with at least one more Hotmail account, wouldn't it? And, perhaps, more importantly, I am getting face-controlled the moment I first try logging in (as soon as I start TB) so it the 1st logging in attempt after minutes or hours.

hotmail has multiple issues.

Perhaps yours is covered by one of the comments in https://support.mozilla.org/questions/1147290

If that fails, it may help to delete cert8.db, key3.db and secmod.db in your Thunderbird profile. (And backup your profile before doing anything drastic)

Thank you for the effort. Unfortunately, none of these apply to my issue, not to mention I have no clue what cert8.db, key3.db, and secmod.db are. I don't use POP (but imap) and would prefer a solution where I do not start a new accoubt because I cannot access my old one. I am fed up doing this with past security screw-ups of both MS and Google (hotmail and gmail) and both of them whistling indifferently, dumping their failure on us.

However, here is my latest and solution (drum roll):

(1) TB installed in my Windows 8.1 tablet worked fine (I accessed all my accounts as if nthng was wrong) (2) after that, trying w/ my main pc (win7) was the same (same Hotmail account not working) (3) a few minutes ago the main PC TB was updated from 45.4.0 to 45.5.0 and ... voilà! All is back to normal!

Don't know if this will help or not but I have had this issue with Yahoo. Yahoo got hacked some time ago and stepped up their security levels and how you can access your email account from third party email apps like Thunderbird. I suspect where one goes the others follow and I wouldn't be surprised if Hotmail has ramped up their security levels.

Can you access the email account directly through the website? If you can then there are probably some hoops you're going to have to jump through to get things right. I have AT&T as my ISP and my long-standing email accounts are on Yahoo ...those accounts work fine. The Yahoo accounts I've set up independent of AT&T are the ones, as I write this, giving me grief. But I did find the solution here in the forum. For you and Hotmail, here's what a little search reaped from Mozilla:

https://support.mozilla.org/en-US/kb/thunderbird-and-hotmail

And hot off the press we have this:

https://support.mozilla.org/en-US/questions/1147268

Hope this helps.