When you use the Samsung Galaxy S9 to send emails via the built-in email app, a signature is automatically attached to it. It says "Sent by my Samsung Galaxy" ex works. If you want to change this signature or deactivate it completely, please proceed as follows:
1. Open the app "E-Mail"
2. Navigate to the three-bar symbol in the upper left corner and then to the symbol for the settings.
3. Select the already created e-mail account by tapping it once. Now go to the "General settings" section.
To deactivate the signature completely, move the slider at "Signature" from "On" to "Off". Alternatively, simply change the existing standard text to your own here. For example your contact details.