When you create a legacy email template in the template library, you can choose to create a Plain Text only email or an HTML & Plain Text email. You are able to copy / paste an HTML email message into the Plain Text editor, but will need to make some adjustments to ensure all links and merge field s are functioning properly. Note that pure, plain text emails are not available in the campaign builder. And, plain text emails cannot be tracked for open rates.
Go to Marketing > Templates
Select Email as the template type.
Enter the template Title, the From Email Address, and the Subject Line.
Choose the Plain Text (no graphics) option to use the plain text editor to create the message.
Scroll down to the plain text editor to type or paste in the email message.
Click on Merge to customize merge fields and merge links.
Signature Merge Field
Be sure you use the proper signature merge field. You want the plain text signature merge field, ~LoggedInUser.Signature~ or ~Owner.Signature~, NOT the HTML signature merge fields (~LoggedInUser.HTMLSignature~ or ~Owner.HTMLSignature~.)
Mark the template as Ready and click the Save button.
Click on the Save & Send Test button to send yourself a copy of the email you just created.
Note: If you are sending both HTML & Plain Text, you may need to temporarily set the Type to Plain Text to test the Plain Text version of your email.