Motorola Moto G — Why has my email sending stopped working over the network?

Hi, up until a few weeks ago everything was working fine. My emails via my 3rd party client have stopped sending over my network, they work fine while conected to wifi. Both my gmail accounts work over network and wifi. It is only this one email account that doesn't send over network.
I have factory reset my phone and reinstalled everything. As I said everything was working fine before. My email provider has said everything is fine his end and so have my service provider. My wife has the same issue, we have motorola g's . should i try my card in another phone ?
Many thanks