My email will not send properly on IPAD And Mac Mail.

All of a sudden yesterday and still today when I send an email from iPad or Mac Mail on my Mac, the mail will not reach its recipient/destination. It shows sent, plays the little airplane noise, ends up in sent box, syncs to other devices sent box, etc... But never ends up in the appropriate in box. If I log into icloud using a browser and send it from there it works fine. This is only when I use a device.

Any Suggestions???

Thanks

Mike