When you start typing an e-mail address in the To, Cc or Bcc field, GMX automatically searches for appropriate entries from your contacts. Click an address to select it. If the address you want is not suggested, simply continue typing it in.
In addition to your contacts, GMX will also suggest unsaved contacts whom you have e-mailed within the past 90 days. These addresses will be deleted automatically after 90 days if they are not used again. For this reason, always save important contacts. If you do not want GMX to suggest unsaved contacts, you can deactivate this function in the sending options.