Hi Ann
Usually the error message of the sender address being rejected by the server means that the mail server you're trying to use cannot authenticate the email address as permitted to use the server.
What I'd do first is make sure you can sign in to your Tiscali mailbox via an Internet browser. Check you can send and receive ok by composing and sending the same mailbox a mail message.
Is the tiscali email account on your iPad set up to use the tiscali mail server?
Setting up TalkTalk email on iPad You'll need tiscali settings that are here Email settings - IMAP & POP3
To appreciate my help . . . If I offered a solution Best Answer