I am not familure with computer talk.
I am using windows 10 and Outlook
I get a 'warning' message - cant send.
'Address had permanant fatal errors'
..temp defered due to user complaints.
These people are my friends and do not understand why the don't receive some emails from me?
Has this just started happening or has it been happening for some time?
Do the mails to Yahoo users sometimes go through ok or is every one rejected?
If you are on NBN, you might try turning the wifi router off for a couple of minutes, then back on. Your connection might get a different ip address which isn't being blocked. (The blockage is possibly at Yahoo and the TPG server is saying it can't send the email.)