my wife & I use our own email id's. as aliases to a prime user (my wife's formal name) all in TPG email. I can send email to her, but she cannot send email to me (this started yesterday after working for more than ten years).
She can send email to a GMAIL account that I have for emergencies, which I can then forward to my TPG email a/c and that works.
I notice that GMAIL flags a comment that it's unable to verify the address of the sender, but apart from that there are no indications of any problems.
This condition is the same whether we use our Thunderbird mail clients or TPG Post Office to send and receive mail.
We've checked spam folders but nothing shows up there.