Hi Sue89
First you will need to identify which platform you are on. You can do this by logging into email.telstra.com
And seeing if what matches here - https://www.telstra.com.au/support/category/email/other/how-to-identify-what-platform-your-email-is-on
You can then find the platform specific setting for POP3 and SMTP here - https://www.telstra.com.au/support/category/email/set-up/imap-pop-and-smtp-information-for-manual-email-set-up
Let me know how you go
-Ashley