: Before buying, take one fully assembled invitation (with liners, ribbons, or wax seals) to the Post Office to get an exact weight. Heavier or "non-machinable" (square/rigid) envelopes require significantly more postage.
Where to Buy Vintage Stamps for Wedding Invitations - The Knot where to buy vintage stamps for wedding invitations
: Generally the most cost-effective option for bulk quantities, though it requires more diligent searching to ensure you are buying unused/mint stock rather than cancelled collector items. Crucial Buying Tips : Before buying, take one fully assembled invitation