Are additional mailboxes linked to home phone/internet account or to mobiles?

[fazd]

Are additional mailboxes linked to home phone account or to mobiles?
We have had the same additional mailboxes for approx 20 years, I am assuming they were linked to our old dialup plan then broadband now NBN. They used to show on the bottom of our MyTelstra account detail screen but no longer appear anywhere.
We are wanting to change our mobiles to a cheaper plan with another company but keeping home phone and NBN with Telstra.
Just concerned, we don't want to lose the email addresses we have had for so long. It would be such a hassle to change everything now.
TIA

[cf4]

All your email addresses are linked to your internet connection.