apple ipad mail other email account set up problem with password or user being continually rejected

Some email providers require the use of App Specific Passwords when accessing mail over IMAP or POP3. If this applies to your email account, you will need to generate a unique password for your iPad email account - that will differ from your normal Account Password. As examples - AOL, Yahoo, Google, Microsoft all use App Specific Passwords when using anything other than their own email client Apps.

If you need to generate an App Specific Password, you’ll need to log-in to your Mail Providers account management webpage - using a web browser - and generate the Password from the appropriate account security page.

More information about AOL’s App Specific Passwords can be found here:

https://help.aol.com/articles/allow-apps-that-use-less-secure-sign-in?guccounter=1

For Yahoo, more information can be found here:

https://help.yahoo.com/kb/SLN27791.html

For Gmail:

https://support.google.com/mail/answer/185833?hl=en-GB

Microsoft:

https://support.microsoft.com/en-us/account-billing/using-app-passwords-with-apps-that-don-t-support-two-step-verification-5896ed9b-4263-e681-128a-a6f2979a7944

What kind of email account (iCloud, Yahoo, gmail, Outlook, AOL, etc)? And does it have 2 factor authentication enabled?

If you go to the site it should have instructions for adding it to an iPhone.