Thanks for raising this with us.
Have you checked if you are able to send out emails using the TPG Post Office? If not, please check it first and let us know if you'll receive any error message.
Is the iPhone the only device experiencing the issue?
Thank you for the information.
We'll raise this with our Post Masters for further investigation.
Please send me a PM with the email address that's affected by the issue also the model of iPhone you are using.