Hello,
Which model iPad?
-Which version of iOS/iPadOS?
-Who is your email account provider?
-Are you using the Mail application, or do you mean the MyMail iOS app?
-If the MyMail app, maybe try deleting and re-installing, then re-add you mail account(s)?
I have never used it, so I don't know if it is not working any longer, discontinued, etc.
C