The annoying thing is its happening [randomly] to a lot of us on here - including me.
The nearest explanation I've had from the BR mail techies ref "why is it happening" is that they and no-one else knows but
it might be an SSL issue with the Yahoo/new BT mail servers.
Annoying as many of us know.
Sadly, for my own part [and others may be able to add to this] all I can tell you that we have had all manner of sign in protocols and landing pages on this forum to get around this issue.
Some work, sometimes, and then not.
If it is an external issue, ie SSL issue on the servers, it is beyond all [customers] reach or ken. All we can really do is keep a beady eye on what works for us now and not venture to look beyond that or seek explanation.
Personally I use Firefox and Chrome with different sign in landing pages on both, run CCleaner on the PC and quite simply hope for the best. I never sign in directly from bt.com but cut and paste the landing pages into my bookmarks. What I have done is forward all bt mail to the gmail account and read them there if btmail is kicking off for me.
For further information I use a mail client anyway to read bt mail [Thunderbird]. Other I had to watch for is that some mail from friends was sent straight to Spam [on btmail] or Bulk on Thunderbird.
Sooner we are all migrated to the new BT in-house mail the better so this basic functioanlity of the Internet can be fully restored and operational. Its 3 years overdue, and no-one knows why that is the case either.
Hope that makes sense, if it helps its a bonus and I'm happy that it does........................
Happened again today! Tried to use outlook on PC to download emails and password rejected. However, rather than go through the arduous process of changing password I used my browser to login to yahoo.com and signed into my email that way. This worked fine and seemed to fix the outlook issue. So that's the temp fix, at least for me, but how long it holds is anyone's guess. Really sub standard showing from the boys at BT over this