RoundCube offers an option to modify a template or signature of the email. The template will be in the email body every time you compose a new email. Hence, you don’t need to add the content manually.
In this guide, I will show you how to create an email template (signature) in RoundCube. I'm using RoundCube 1.4.6 which may look different you are using a different version.
Go to your RoundCube email.
Click on Settings.
Go to Identities and select your email identity (or create a new one).
Click on HTML editing for better experience.
Create your template. Then click Save.
Try to Compose a new email to see how it looks.
Since the signature was made using the HTML editor, it’s you may want to set HTML as the default message editor as well. Go to Settings > Preferences > Composing Messages > Compose HTML messages > always.
This will prevent unintended changes when switching between plain text and HTML editor.