SMS Messages received but not sent in 4.4

Xperia X 4.4.x

I have discovered today that while I have no difficulty receiving messages, any that I send disappear into the vast abyss and are not received at the other end, with no error on my end. The send time shows correctly.

This made my wife very unhappy :frowning:

I am in Thailand using AIS and in this case sending to DTAC