Upgrade to High Sierra killed Mail /Optus Login

Since ‘upgrading’ to High Sierra three of our four Optus a/c passwords are not working. Is there a simple solution, please, or do I have to spend 3 hrs on the phone to Optus? I can’t find anything on-line.

Apple a/c and password still work.

Any help much appreciated.
Thanks

Can you log in via webmail?
https://webmail.optusnet.com.au/index.php/mobile

That would prove whether it’s an account issue or a a Mac OS/ Mail issue.

Thanks Chiateno. I haven’t been on here for a while so missed your post.
Yes, I could log in via webmail and send from there. I think it’s solved now after I pretended to change the password, just reentered the old p/w’s as new passwords. Dunno how it works!