iphone 6 will not sent email through 3G/LTE but will through wifi

My iphone 6 will not sent email through 3G/LTE but will through wifi. This is a new problem which just popped up. The message goes into the sent folder, when I send it; it makes the swoosh sound but it is not received. If I use wifi, it does get received. Also, if I use my provider's webmail ( Fido in Canada) on my computer or another computer at work, it does go through.

I have called my provider 3 times, deleted the account, put it back in, no change. They tell me that if it goes through wifi and the webmail, it is not their server's problem.

Help.....