Unable to send emails from Outlook after enforced password change

[MaisonMontruf]

Hi - Recieved a text (sunday) from BT saying "Strange behaviour on your account we've locked the account to protect you and you need to change your password"  I followed the instructions and changed my password.

Since changing the password I cannot send emails (recieving is fine) via my MS Outlook client(s). This is the error message.

Task 'xxxxxxxx.yyyyyyy@btinternet.com - Sending' reported error (0x8004210B) : 'The operation timed out waiting for a response from the sending (SMTP) server. If you continue to receive this message, contact your server administrator or Internet service provider (ISP).'

I have two PC's and the problem exists on both PC's.  I have 3 btinternet.com emails managed by the Outlook client and the problem is across all of them.  The other two email accounts managed by the same Outlook client are fine and I can send emails from my iPad and a web client.  Its just Outlook that's broken

Nothing has changed here other than changing my BT password.   

Helpful Information

I am a BTPremium user.

Microsoft® Outlook® for Microsoft 365 MSO (Version 2301 Build 16.0.16026.20002) 32-bit

Rebooted my router and PC.

Tested with VPN on and VPN off.

Does anyone have any ideas.

Thank you 

[MaisonMontruf]

Hi Just tidying this up as I hate posts which dont have a conclusion.   
The resolution for this was to delete my account on Outlook and then re add it. (Note if you do this make sure you back up your contacts first).   So that fixed it but 2 days later the problem returned and after a further 2 days it dissapeared.  So I am none the wiser as to what caused this but I feel it must have been a BT server issue.