Related Clues:

• Tamper-resistant, perhaps
• Like good alibis
• Shut up tight
• Like some rulings
• Like some alibis
• Part of SWAK
• Ready for mailing, as an envelope
• Closed, as an envelope
• Ready to mail
• Fastened shut
• Closed tight
• Shut tight
• Unbreakable, as an alibi
• Like diplomatic pouches
• Solid, alibiwise