When you preview your card, you'll see "For: (Guest Name)" and/or "your guest name will go here". If you send yourself a Free Test Preview, it will be populated with the sender/host name you entered in your event details (or the event name if you don't have a host name entered). Please note that we don't have a way to preview each recipient name on the envelope at this time.
The names you add to your recipient list will automatically populate on the front of the envelope. If you leave the "Name" field blank on a Card that collects RSVPs, your event title will appear instead. If you leave the “Name” field blank for Cards not collecting RSVPs, the subject line of your sending will populate on the envelope instead.
In either instance, you can choose to customize the font for the envelope text. From your Card's Create/Edit page, click or tap on the envelope to select it, and then choose the Flip icon 
From there, you can tap or click on the text to select it, and choose the font of your choice from the Envelope fonts panel that appears:
There is not a way to choose a different color for the envelope font at this time — we hope to add this feature in the future!
Related Articles:
Editing, Removing, or Adding a Envelope and Liner
Previewing Your Design