In order to see any wedding invitations that are not deliverable by the Post Office, you will need to include a return address on them.
You can actually plan for this at the time you have your invites printed. There is usually an option for having a return address printed on the back flap of your mailing envelopes for a small extra charge. This convenience may be worth the cost since it eliminates having to later handwrite it on the envelopes or attach return labels.
The return address, when professionally printed on the envelopes, typically includes just the two-line mailing address, no name. All words within the address are completely spelled out including the state name.
As shown below, you may even choose to match the font on your envelope to the typestyle of your invitation verse.