postmap
Create and query Postfix lookup tables
TLDR
Create hash database from text file
SYNOPSIS
postmap [options] [filetype:]name_
DESCRIPTION
postmap creates and queries Postfix lookup tables. It converts plain text files containing key-value pairs into indexed database formats (hash, btree, dbm) for efficient lookups by the Postfix mail system. Common uses include virtual alias maps, transport maps, and access control tables.
After editing a text lookup file, postmap must be run to rebuild the corresponding .db file that Postfix actually reads. The query mode (-q) allows testing individual lookups, and the show mode (-s) displays all entries, both useful for verifying that mappings work as expected before applying them to live mail delivery.
PARAMETERS
-q key
Query for key.-s
Show all entries.-d key
Delete key.-i
Incremental mode.-N
Include newlines in values.-w
Wait for locked files.
EXAMPLES
postmap /etc/postfix/virtual
# Create transport map
postmap hash:/etc/postfix/transport
# Query specific entry
postmap -q "user@example.com" /etc/postfix/virtual
# Show all mappings
postmap -s /etc/postfix/virtual
# Delete entry
postmap -d "olduser@example.com" /etc/postfix/virtual
FILE FORMAT
user@example.com localuser
@example.com catchall@other.com
CAVEATS
Run postmap after editing text files. Postfix reads .db file, not text. Use postmap -q to verify.
HISTORY
postmap is part of Postfix, the mail transfer agent created by Wietse Venema as a secure alternative to Sendmail.