Like some envelopes

• Requiring no stamps
• Not requiring stamps
• (Of mail) charged for in advance

Longman Dictionary of Contemporary English Word definitions in Longman Dictionary of Contemporary English
adjective EXAMPLES FROM OTHER ENTRIES ▪ Calendars are available for $10.95 postpaid .

Wiktionary Word definitions in Wiktionary
a. 1 paid in advance (gloss: used especially of mail items) 2 paid after the service (gloss: used especially of cellular phones)

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
Postpaid \Post"paid`\, a. Having the postage prepaid, as a letter.

WordNet Word definitions in WordNet
adj. used especially of mail; paid in advance [syn: prepaid ]