vdukhovni/postfix Documentation

The qmqp-sink utility is a parallelized test server used to measure QMQP client performance. It listens on a specified host/port or UNIX-domain socket and receives messages from the network, which it then discards. It is designed to be used as the complement to the qmqp-source program.

Note: This is an unsupported test program. Compatibility between successive versions is not guaranteed.

# Example: Listen on a network host and port with a backlog of 128
qmqp-sink inet:localhost:10025 128

# Example: Listen on a UNIX-domain socket with a backlog of 128
qmqp-sink unix:/tmp/qmqp.sock 128

The postsuper command is used by the superuser to perform maintenance tasks on the Postfix mail queue. While unprivileged users can use postqueue for listing or flushing, postsuper is required for destructive or structural operations like deleting, holding, or requeueing messages.

By default, operations like -s (structure check) or -p (purge) apply to all Postfix queue directories, including incoming, active, deferred, hold, bounce, defer, trace, and flush.

The qshape program provides administrators with a distribution of Postfix queue messages based on time (age) and by sender or recipient domain.

Permissions Requirement: Because qshape must read queue directories and files, it must be run as the superuser or as the mail_owner specified in main.cf (typically postfix).

Basic Usage: By default, qshape displays the combined distribution of the incoming and active queues, categorized by recipient domain using a geometric age sequence.

The postmap command is used to create, query, or update Postfix lookup tables. It can transform a plain text source file into a database format (like hash:, btree:, or lmdb:) or perform direct queries against existing maps.

Basic Usage Patterns:

• Create/Update a table: postmap [options] [file_type:]file_name
• Query a single key: postmap -q key file_type:file_name
• List all elements: postmap -s file_type:file_name
• Remove an entry: postmap -d key file_type:file_name

When updating a table, postmap places an exclusive advisory lock on the entire table to prevent issues with concurrent processes.

postmap hash:/etc/postfix/access

The flush server is a Postfix daemon that maintains a record of deferred mail organized by destination. This mechanism improves the performance of SMTP ETRN requests and their command-line equivalents (sendmail -qR or postqueue -f) by allowing the system to quickly identify which destinations have queued mail without scanning the entire queue.

Key Concepts:

• Destination: Defined as the part on the right-hand side of the right-most @ in an email address.
• Logfiles: The server uses per-destination, append-only logfiles located in /var/spool/postfix/flush. These files contain the queue IDs of deferred mail. A logfile is truncated when delivery is requested for that destination.
• Eligibility: Only destinations specified in the fast_flush_domains parameter are tracked.
• Execution: This program is designed to be managed by the master process manager.

A generic table specifies address mappings used during mail delivery. It is primarily used by the smtp client to transform local mail addresses (e.g., user@localdomain.local) into valid Internet mail addresses when sending mail across the Internet. This is particularly useful for systems that do not have a valid Internet domain name.

Unlike canonical mappings (which apply when mail is received), generic mappings apply when mail is sent and affect both message header addresses and message envelope addresses.

The tlsmgr(8) daemon is a persistent Postfix process that manages two primary functions:

1. TLS Session Cache Management: It stores and retrieves TLS session cache entries requested by smtpd(8) (server) and smtp(8) (client) processes. It also handles the periodic removal of expired entries.
2. PRNG Pool Management: It manages the Pseudo Random Number Generator (PRNG) pool. It provides entropy to seed the internal PRNG pools of smtpd and smtp processes. The pool is seeded from an external source (like /dev/urandom or an EGD), updated with data from TLS cache entries and the time of day, and its state is periodically saved to an exchange file.

Security Note: tlsmgr is not considered security-sensitive. It does not "trust" the data it manipulates, and it does not touch the actual contents of cached TLS entries, except for using them to seed the PRNG pool.

The Anvil server is a Postfix component designed to maintain statistics about client connection counts and request rates. It is used to defend against clients that attempt to overwhelm the server with too many simultaneous sessions or too many successive requests within a specific time interval.

Anvil is designed to run under the control of the Postfix master server and maintains an in-memory table of recent client requests. It does not keep persistent state. To reduce memory usage on high-traffic systems, you can decrease the time unit over which state is kept.

postlogd is the Postfix internal log server. It is responsible for logging events on behalf of other Postfix programs when the maillog_file configuration parameter is set to a non-empty value.

Instead of every Postfix program writing directly to a file, they send their logs to postlogd, which manages the centralized log file. This allows Postfix to handle logging to a specific file even when individual programs are running with restricted permissions.