For tracking reasons you can only send HTML emails in Mailster. If you like to send plain text messages there is a simple trick you can do.
Create a new campaign and switch to codeview in the option bar of the editor. This will reveal the raw HTML of you template.
Now remove all it’s content by selecting everything and hitting the delete button on your keyboard.
Write your content into the empty line. You can still use HTML tags.
If you switch back from the codeview you’ll get a plain text like template. Your content is now editable and you can edit it like other multi line content fields.
Your template is now still a HTML template (with all it’s advantages) but it will looks much like a plain text campaign.
This template will work just fine on mobile as well on desktop, will support your HTML and you can still use your tags.