How do you do it? Send it flat, or bend it in half?
Flat - never bend a postcard in half. It may require extra postage depending on where you’re mailing from.
Edit to add… Just noticed you’re from the US… You will need a Forever stamp if mailing domestically. International rates remain the same as usual.
What kind of panoramic cards are you talking about? If it’s just a long (but else normal) card: don’t bend it! Just send it as is. But there are certain sorts of panoramic cards that are meant to be bent and closed off! Those I would bend for sure.
Here’s an example of a panoramic card that was made to be bent:
It is not the kind that has folding instructions. Thank you!
@Siggy419
You don’t need to fold and seal it if it is under the USPS maximum letter size 6-1/8" by 11.5"
[Domestically, don’t forget letter rate when it is bigger than the USPS postcard max 4-1/4" by 6"]
Any taller or wider than that maximum letter size I worry it is too flimsy to make it in one piece, and you’re into the large envelope rate – a significant price jump!