Can not send mail "null" user name or password are

"This pop-up occurs when I try to send an Em from any of four account addresses I have??? It never sends them."

-------

Try this site: If you can’t Send eMail on your iPhone, iPad, or iPod touch - Apple Support. Remove these accounts, then add them back.

"Can not send mail "null" user name or password are incorrect: What is wrong? Checked all Em accounts and setting are right."

-------

"Null" Entered Data:

Enter your eMail and password. If you ready have, apparently, it is not seeing what you are entering. Any success?