The configuration and use of any outgoing server address (SMTP) may not be supported due to several factors including, but not limited to, the inability for the outgoing server (SMTP) to authenticate users (whether by IP or username/password) that are not directly connected to that Internet Service Providers(ISPs) network.
This is usually your HOME wi-fi and you are not connected to it because you are on your iPad away from the house. This is mainly done to prevent unsolicited users from sending SPAM via the ISP's servers.
If you are interested you can obtain that information directly from the email provider. This article has a great temple that you can use to ask all necessary information from the provider including "If you use your ISP’s own email service (instead of a third-party such as Gmail), sometimes it may not work if you use another Internet access point, such as a cafe with wireless Internet. Ask your email provider if the settings they give you will work on other networks."
What to ask if you're having issues sending, receiving, or configuring Mail
http://support.apple.com/kb/HT1277