Miscellaneous topics that do not fit into specific categories.
Have you tried deleting the account & re-adding it?
Are you running any third party antivirus &/or VPN software?
If you set up the account manually then double check the incoming & outgoing servers & ensure that the security is set to OAUTH 2.0 if supported, if not then you may require an app specific password which is used instead of the account password.
Incoming Mail Server: imap.telstra.com
Outgoing Mail Server: smtp.telstra.com
Outgoing Mail Port: 465 or 587
Authentication: Yes
Encryption: SSL enabled.
App specific password:
https://www.telstra.com.au/support/email/app-specific-password
https://learn.microsoft.com/en-us/answers/questions/5830684/how-to-fix-outlook-fix-error-0x800ccc0e
Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information. Watch out for ads on the site that may advertise products frequently classified as a PUP (Potentially Unwanted Products).
Please do not download any repair tool which may be offered by this site other than the ones I mention/recommend.
Thoroughly research any product which is mentioned here before you decide to download and install it.