What to try when "The SMTP server is not responding" and the network connection is good and the correct info has been entered in the "Outgoing Mail Server" field?

If you're sure (after contacting your email provider) that the SMTP/IMAP or POP3 parameters are correct, and if you're using Apple Mail app, try to delete that email account from your iPad, restart the device, then re-add the account.

If you're using a different mail app, please contact their support team and ask them.

Regards

Giulio