General Resource Control

This page provides access to the various memory and process limits for the Postfix processes (Figure 10-6). It is rarely necessary to alter the values on this page, except for highly loaded servers or very low resource machines.

Figure 10-6: General resource control

Max size of bounced message

This option limits the amount of the original message content in bytes that will be sent in a bounce notification. This option correlates to bounce_size_limit and defaults to 50000.

Max time for delivery to external commands

When delivering mail to an external command (rather than via direct mailbox delivery), Postfix will wait this amount of time for the delivery to complete. If this value is to be set to a high limit (3600s or more) the value of Timeout for I/O on internal comm channels in General Options must also be increased. This option correlates to the command_time_limit directive and defaults to 1000s.

Max number of Postfix child processes

This option limits the number of child processes that Postfix will spawn. On high load servers the default may be too low and may need to be raised to as much as 500 or more. More likely, for most environments, 50 is more than adequate and may even be overkill. For example, on dial-up or consumer broadband serving one to ten users, a more appropriate limit might be 10. If in doubt, leave it at its default unless it causes problems. This option correlates to the default_process_limit directive and defaults to 50.

Max number of addresses remembered by the duplicate filters

While expanding aliases and .forward files Postfix will remember addresses that are being delivered to and attempt to prevent duplicate deliveries to the same address. This option limits the number of recipient addresses that will be remembered. It corresponds to the duplicate_filter_limit directive and defaults to 1000. There is probably no compelling reason to increase this value.

Max attempts to acquire file lock

This option limits the number of attempts Postfix will make when attempting to obtain an exclusive lock on a mailbox or other file requiring exclusive access. It corresponds to the deliver_lock_attempts directive and defaults to 20.

Time in seconds between file lock attempts

Postfix will wait a specified time between attempts to lock a given file, after a failed lock attempt. This option configures the deliver_lock_delay directive and defaults to 1s.

Max attempts to fork a process

If Postfix attempts to fork a new process and fails, due to errors or a lack of available resources, it will try again a specified number of times. This option correlates to the fork_attempts directive and defaults to 5.

Time in seconds between fork attempts

Postfix will try to spawn a new process a specified time after a failed attempt. This option correlates to the fork_delay directive and defaults to 1s.

Max memory used for processing headers

This option limits the amount of memory in bytes that Postfix will use to process message headers. If a message header is too large to fit into the memory specified, the headers that do not fit into memory will be treated as part of the message body. This option correlates to the header_size_limit directive and defaults to 102400.

Max memory used for handling input lines

This option limits the amount of memory in bytes that Postfix will use to handle input lines. And input line is any line read from an :include: or .forward file. In order to prevent the mail server from using excessive amounts of memory, it will break up these files into chunks of this length. This option correlates to the line_length_limit directive and defaults to 2048.

Max size of a message

This option limits the size in bytes of a message that will be delivered, including the message envelope information. This limit should be set high enough to support any email messages your users will need to be able to send or receive. This option correlates to the message_size_limit directive and defaults to 10240000.

Max number of messages in the active queue

This option limits the number of messages that can exist in the message queue at any given time. It correlates to the qmgr_message_active_limit directive and defaults to 10000.

Max number of in-memory recipients

This parameter limits the number of in-memory recipient data structures. This memory contains the short-term dead list, which indicates a destination was unavailable when last contacted, among other things. This option correlates to the qmgr_message_recipient_limit directive and defaults to 1000.

Min free space in the queue file system

Postfix will refuse mail if the filesystem on which the queue is located has less available space in bytes than the value set in this option. This option correlates to the queue_minfree directive and defaults to 0.

Max time after which stale lock is released

This option configures how old an external lock file may be before it is forcibly removed. This option correlates to the stale_lock_time and defaults to 500s.

Time in seconds between attempts to contact a broken MDT

This option configures the time in seconds between the queue manager attempts to contact an unresponsive mail delivery transport. This option correlates to the transport_retry_time and defaults to 60s.