Save the date postcards

Send without return label. You'll put those on the invite. I did postcards, just made sure website was on it, get postcard stamps and voila!

If you feel confident that you have the correct addresses for your guests, it's totally fine to send postcards without a return address. If you're uncomfortable doing that, you can edit the postcard to include a return address on the card, but it does look a bit crowded:

I did postcards and didn’t put a return label.
Most people received it.

Like PP mentioned, if you’re not comfortable not having a return address, I would ask to have them add your return address. Or if you know how to use illustrator and able to just purchase the digital file, it’s easy to do on your end— takes about 5 minutes.
I didn’t like the font that the ETSY shop owner was using and she wouldn’t make edits for me so I just bought the digital file for $35, edited myself and printed 125 for $30 (on sale from Vista Print). She was originally charging me $150+.