Unfortunately, it is not possible to add a direct hyperlink to print out a campaign. As a workaround, I’d recommend adding the View in Browser option to the campaign. From there, recipients can then print out emails from their browser.
Option 1: Enable by default for all campaigns
Go to Settings > Campaigns > Default Settings
Enable « Add a ‹ View in browser › link to all campaigns »
Click Save
This will automatically add the link to the top of all future email campaigns.
Option 2: Add manually to individual campaigns
Drag & Drop Editor: Go to the Style tab → Template section → Activate « View in browser »