Microsoft changed a load of things recently, but was not exactly offering the information in an easy to find location. It's very good at offering info on using it's own products and basic info on what server to use for email clients, but not so good at telling you what password are now used or what it will allow via smtp.

I located this from a Microsoft website: Email addresses and phone numbers associated with your Microsoft account are called aliases and they use the same contacts, online storage, subscriptions, and account settings. You can use any of your aliases to sign in to Microsoft services or your Windows and Xbox devices, and you can select any of them for sending and receiving email. Your aliases share a single password.

That's where I found out whatever is set up as password for Microsoft account now has to be used for all alias mail accounts. But it seems you can only choose to send from something other than primary if using Exchange or directly via webmail.

Now the Microsoft Account contains email addresses/mail account which are all considered as alias accounts. So the password you use to access Microsoft Account must now be the same password used in all the outlook.com, hotmail.com, live.com, msn.com and any other mail address that uses the outlook server.

You can choose whatever email address you like to be the 'primary' email address, but Microsoft will now only allow you to send via smtp using that primary email address.

You must set all the above up via webmail access to Microsoft account.

In Thunderbird You will need to have cookies enabled Settings > Privacy & Security WEb Content Select 'Accept cookies from sites Accept third party cookies 'Always'

'Authentication Method' must be 'Oauth2' for incoming and outgoing

If you have eg: two hotmail accounts, then whilst they get created separately you will need to set up all accounts to use Outgoing Server SMTP as only whatever account you set up as primary.

So if have eg: hotmail Acc1 and hotmail Acc2 AND Acc2 is set up as primary then: Smtp outgoing server for both Acc1 and Acc2 will use Acc2 email address.

In which case, in Account Settings, remember to set up Acc1 'Reply-to Address' email address as Acc1 email address because it will be sending using Acc2 email address and you may not want replies going to wrong account.

So - it's important to set up a primary account which you know is ok for sending purposes.

Somehow I fixed this issue here's steps:

• First itemrstly;

I went to the settings in the Microsoft account and revoked access Thunderbird under allowed APPs.

• Secondary;

[|Forwarding Options under settings on outlook]

I went to the page, turned off pop and imap settings, saved it, then turned it back on and selected ‘Let apps and devices delete messages from outlook’.

• Tertiary;

I deleted thunderbird app with 'Revo Uninstaller' deleted every reg entry & local folder & saved profiles under %appdata%

• Quaternary;

I have given full permission to all hotmail, outlook, account.live, microsoft cookies under Thunderbird Settings > Privacy and Security > Privileged Cookies.

• Last but not least;

I reinstalled Thunderbird, entered the mails one by one. If I get an error on any mail and non-synchronised email addresses, I did steps 1 and 2.

Somehow this fixed my issue.