The sorted database format ensures that user records are clustered together. Meta-information is always stored with a leading colon.
Field names define both the syntax and semantics of the value.
There may be multiple values of this record. In particular, mailing lists will have one maildrop record for each user on the list. For each outgoing name, there should be an appropriate maildrop record for that name to allow return mail. Changes any mail sent to this address to have the indicated envelope sender. This is intended for mailing lists, and will normally be the name of an appropriate -request address.