If you search in google e.g. for this two words: Yahoo #MBR1236 , you will find a lot of people complaining about Yahoo login problems - mostly intermittent, - from different networks, with different software (including desktop Thunderbird).
In some cases the situation is different (a person didn't enter the full e-mail address for login, etc.), but many cases are very similar (and seeming unresolved).
If the culprit is of technical nature (i.e. packets, connectivity, server, software, ...), I'd be putting the blame on Yahoo.
After all, - Aquamail does connect to Yahoo's IMAP server from Orange, - so Orange provides connectivity to the server. And Yahoo does not authenticate you.
Where Orange might be at fault is if Yahoo enforces some policy against Orange, i.e. due to heavy spamming or hacking or whatever activity originating from their network.
In any case, - those are problems that are not related to Aquamail per se. And if the suggestions that Kostya offered as possible workarounds do not work, I'd recommend considering dropping Yahoo as a provider.
By the way, - have you tried the last possible workaround suggested by Kostya?
"
In incoming server settings, you could try changing the login method from "auto" (which will pick SASL PLAIN for Yahoo) to "SASL LOGIN".
No idea it that'll help or what, but it's a different IMAP command to log in.
I pointed to you which that option is in your screenshot:
Authentication: "Choose Automatically".