certificate of posting
noun[C]
ukuspluralcertificates of postingCOMMUNICATIONS
in the UK, anofficialdocumentfrom thepostoffice, used toprovethat you havemailedsomething on aparticulardate:
In theeventyouritemislostordamagedin themail, you will have topresentastampedandsignedcertificateofpostingwithyourclaimforloss.