Cannot Send Mail - sender address invalid WHY ??

Bigpond email on Apple Mail app, POP account info, incoming mail server info (receiving emails fine) and outgoing mail server info all correct (I think), but cannot send an email from an Apple device. Bigpond email sending and receiving fine via outlook on PC, iPad and iPhone, seems an issue with Apple settings?

INCOMING MAIL SERVER: mail.bigpond.com

OUTGOING MAIL SERVER: smtp.telstra.com, port 465 (changed from mail.bigpond.com, port 587)

Are the details incorrect? Is there an update? Is this a Tesltra issue or an Apple Mail issue?

Apple iPhone 15 Pro iOS17.5.1