it is not clear if you are trying to set up an iCloud email address, a Plusnet email address or both ? The settings for an iCloud email address should be automatically set when you sign into iCloud on your iPad. If you are having trouble with this I would sign out of iCloud and then sign back in to see if the problem is resolved.
If you are having problems with a Plusnet email address then delete the account you have already set up and reinput the details. From Settings > Mail, Contacts, Calendars click on Add Account and then select 'Other'. Under the 'Mail' heading select 'Add Mail Account' and enter your name, Plusnet email address, the password for that email address and an identifying description for the account (or leave it as the pre filled default). Click on 'Next' and with the 'IMAP' heading highlighted enter imap.plus.net as the Incoming Mail Server Host Name, your Plusnet Account Name and the Password for the email account (which should already be prefilled). In the Outgoing Mail Server settings input relay.plus.net as the Host Name and input the same Account Name and Password as you input for the incoming mail server. Clicking on 'Next' should start Verifying the settings and you will then get a message "Cannot Connect Using SSL. Do you want to try setting up the account without SSL ?" to which you should select 'Yes'. Verifying will then continue and you may get the same message about SSL to which you should select 'Yes' again. When verifying is complete you should have an option for 'Mail' and 'Notes" You only need to have 'Mail' switched on (which it is by default) so you can go ahead and move the 'Notes' slider to 'Off" (no green colour shows). Then click 'Save" and 'Account Added' should appear.
If you are still having problems then it is likely that you are using an incorrect email address and / or password. If you are using your default Plusnet email address (in the format of dafaultname@accountname.plus.com) then the Username to input on the iPad should be accountname and the password should be your main Plusnet Password. If you have set up an additional Plusnet Mailbox (in the format of name@accountname.plus.com) then the Username to input on the iPad should be accountname+name and the password should be that set up for the new Email Mailbox.
