Which industries use custom printed envelopes?

Nearly every industry, with different envelopes for different jobs:

• Accounting and payroll: security window envelopes and #9 return envelopes
• Healthcare, insurance and utilities: self-seal security and window envelopes
• Legal and professional services: linen #10 envelopes and 9x12 document envelopes
• Real estate and mortgage: 9x12 closing envelopes and A7 holiday card envelopes
• Marketing and retail: 9x12 and 6x9 catalog envelopes, and addressed #10 envelopes
• Nonprofits and churches: #10 appeal and #9 reply envelopes, and A7 or A9 gala invitations
• Schools and universities: 9x12 admissions packets and A7 graduation announcements
• Weddings and events: A7 invitation and A2 RSVP envelopes
• Photographers and online shops: A6 envelopes for 4x6 prints and inserts