Mail documents you need to keep private in these No. 6 security envelopes with a lining to shield your information. Press-it Seal-it, self-adhesive closure makes sealing the envelopes easy. Simply peel the strip, and the envelope instantly seals with no licking.Mail documents you need to keep private in these No. 6 security envelopes with a lining to shield your information. Press-it Seal-it, self-adhesive closure makes sealing the envelopes easy. Simply peel the strip, and the envelope instantly seals with no licking.