Email suddenly stops working on iOS devices

I have been using email on my iPad 2 and iPhone 5 for over a year.

Two days ago, it stopped receiving email.

The error message I get is

"Cannot get mail. Password or username is incorrect."

Except that the email on my MacBook Pro works fine using Thunderbird, and I have no trouble accessing the web based email using a PC.

In fact, I was even able to send myself a test email from the iPad to my gmail account.

Any ideas, suggestions. I re-booted each device twice to no effect,

Thanks,

Steve