Manyedmana,
It's great that the clarification you received explaining what SMTP means simplified things for you. As for your follow-up questions, using Cellular Data to browse the internet should be fine. If you have further questions regarding issues pertaining to Cellular Data, please reach out to your wireless carrier for continued support since they are best suited to answer your inquiries directly.
Lastly, when it comes to browsing the web over WiFi, we recommend using your best judgment to determine if it is safe or not for you to join, as we cannot provide feedback since all WiFi networks are configured differently.
Thank you for reaching out to the Apple Support Community.
Cheers!