There are certain guidelines on how to address wedding invitations with no inner envelope. It used to be traditional for invitations to be mailed with two envelopes – an inner envelope & an outer envelope. Now with the newer trendy styles of wedding invitations such as pockets, self-mailers and seal and sends, that is not always the case anymore.
If there is an absence of an inner envelope, all your invitation pieces are directly inserted into the mailing envelope with all individual guest names being listed as part of the mailing address. For self-mailers and seal and sends, they are wrapped up into their own self-mailing piece for proper addressing.
Please use this link to read about the proper guidelines for how to address wedding invitations for mailing.