Apple mail not recognising new password but other clients OK

Changed password on one of my email accounts and, all of a sudden, none of my Apple products recognise it. Have tried signing in (having changed password) on iMac, iPhone & Ipad and all say either password or user name is incorrect.

All other accounts are still working fine and if I use a different email client to access the account I changed then I can access that account too....just not on any Apple device.

Have tried multiple times either copying password from password manager or entering manually. Have also tried deleting account and setting up again - same thing happens.

Driving me nuts! Can anyone help please?