IMAP stands for "Internet Message Access Protocol" and is a protocol for receiving e-mail. This protocol requires a stable Internet connection. IMAP allows you to access your mailbox in real time with an e-mail program of your choice. Any actions (e.g. delete, move an e-mail etc.) will be conducted directly in your GMX mailbox. This means that you can access your e-mail on another computer, a smartphone, or at https://www.gmx.com/ at any time. The status of your e-mail is the same on all devices.
SMTP stands for "Simple Mail Transfer Protocol" and is a protocol for sending e-mail. SMTP transmits your e-mail from your e-mail program to a server and then forwards them to the respective recipient.