Postfix Overview - Introduction - SCN Research

Postfix Configuration - Resource Controls
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Postfix Configuration - Resource Controls
Up one level | Basic Configuration | UCE Controls | Rate Controls | Resource Controls | Address Manipulation
Introduction
The Postfix system is designed to run within a finite memory budget. To this end, there are configurable limits
on the size of in-memory objects such as text line fragments, on the number of instances of such objects, and on
the time an operation may take. In addition, strategies are in place for dealing with resource exhaustion. The
idea is to keep running under conditions of stress, without making the problem worse.
• Object size limits
• Object count limits
• Time limits
• Acquiring exclusive file locks
• Error recovery
Object size limits
The first step towards a fixed memory resource budget is to limit the size of each in-memory object. Once the
size of in-memory objects is limited, total memory consumption is limited by limiting the number of object
instances. Simple, no?
line_length_limit (default: 2048 bytes)
How long a line of text can be before it is broken up into pieces. All Postfix perimeter programs (SMTP
server, SMTP client, local pickup and local delivery) enforce this line length limit when reading data
from an untrusted source. Long lines are reconstructed upon delivery.
header_size_limit (default: 102400 bytes)
How much text may be carried in a multi-line message header. Header text that does not fit in
$header_size_limit bytes overflows into the message body. This limit is enforced by the cleanup header
rewriting code.
extract_recipient_limit (default: 10240 recipients)
How many recipients Postfix will extract from message headers before it gives up. This limits the damage
that a run-away program can do with "sendmail -t".
The following parameters restrict the use of file system storage:
message_size_limit (default: 10240000 bytes)
The maximal size of a Postfix queue file, including envelope information (sender, recipient, etc.).
queue_minfree (default: no restriction)
How many bytes of free space are needed in the queue file system. The SMTP server declines inbound
http://www.porcupine.org/postfix-mirror/resource.html
6/26/01