Postfix Overview - Introduction - SCN Research

More documents

Recommendations

Info

Postfix Overview - Goals and Features single Postfix lookup table. Other mailers usually need multiple levels of aliasing or redirection to achieve the same result. Page 2 of 2 • UCE control. Postfix can restrict what hosts can relay their mail through a Postfix system, and supports restrictions on what mail is allowed to come in. Postfix implements the usual suspects: blacklists, RBL lookups, HELO/sender DNS lookups. Content filtering hasn't been implemented yet. • Table lookups. Postfix does not yet implement an address rewriting language. Instead it makes extensive use of table lookups. Tables can be local dbm or db files, or networked NIS or NetInfo maps. Adding support for other lookup mechanisms is relatively easy. Up one level | Introduction | Goals and features | Global architecture | Queue Management | Security http://www.porcupine.org/postfix-mirror/goals.html 6/26/01
Postfix Overview - Global Architecture Page 1 of 2 Postfix Overview - Global Architecture Up one level | Introduction | Goals and features | Global architecture | Queue Management | Security Introduction Some mail systems such as Sendmail are implemented as one large monolithic program that does everything. One large program certainly makes it easy to share data between different parts of the system. Unfortunately, one large program also makes it easy to make fatal mistakes. Other mailers such as qmail use a rigid hierarchy of programs that run other programs in a fixed order and throw them away after use. This approach gives better insulation, at the cost of some process creation overhead and inter-process communication. The additional cost can be kept within acceptable limits by partitioning the work in a sensible manner. Postfix architecture Postfix is based on semi-resident, mutually-cooperating, processes that perform specific tasks for each other, without any particular parent-child relationship. Again, doing work in separate processes gives better insulation than using one big program. In addition, the Postfix approach has the advantage that a service such as address rewriting is available to every Postfix component program, without incurring the cost of process creation just to rewrite one address. By the way: I do not claim that Postfix is the only (mail) program using this approach. Even in this relatively young discipline it is hard to come up something new that no-one ever did before. Postfix is implemented as a resident master server that runs Postfix daemon processes on demand: daemon processes to send or receive network mail messages, daemon processes to deliver mail locally, etc. These processes are created up to a configurable number, are re-used for a configurable number of times, and go away after a configurable amount of idle time. This approach drastically reduces process creation overhead while still providing the good insulation from separate processes. Postfix is intended to be a Sendmail replacement. For this reason it tries to be compatible with existing infrastructure. However, many parts of the Postfix system, such as the local delivery program, are easily replaced by editing an inetd-like configuration file. For example, the plan is to provide an alternate local delivery program that runs at a fixed low privilege, for POP/IMAP users that never log into the shell, and that may not even have a UNIX account. As a result of this architecture, Postfix is easy to strip down to the bare minimum. Subsystems that are turned off cannot be exploited. Firewalls do not need local delivery. On client workstations, one disables both the smtp listener and local delivery subsystems; or the client mounts the maildrop directory from a file server, and runs no resident Postfix processes at all. Communication between Postfix processes The core of the Postfix system is implemented by a dozen semi-resident programs. For privacy reasons, these Postfix processes communicate via UNIX-domain sockets or FIFOs that live in a protected directory. Despite this privacy, Postfix processes do not really trust the data that they receive in this manner; just like the contents of Postfix queue files, they merely treat it as gossip. The amount of information passed on between Postfix processes is limited. In many cases, the only information exchanged between Postfix processes is a queue file name and a list of recipients or some status information. http://www.porcupine.org/postfix-mirror/architecture.html 6/26/01
Page 1: Postfix Overview - Introduction Pag
Page 6 and 7: Postfix Overview - Global Architect
Page 8 and 9: Postfix Overview - Queue Management
Page 10 and 11: Postfix Overview - Security assista
Page 12 and 13: Postfix Anatomy - Receiving Mail Pa
Page 14 and 15: Postfix Anatomy - Delivering Mail p
Page 16 and 17: Postfix Anatomy - Command-line Util
Page 18 and 19: Postfix Configuration - Basics What
Page 20 and 21: Postfix Configuration - Basics My o
Page 23 and 24: Postfix Configuration - UCE Control
Page 33 and 34: Postfix Rate Controls Page 1 of 4 P
Page 35 and 36: Postfix Rate Controls The defer_tra
Page 37 and 38: Postfix Configuration - Resource Co
Page 39: Postfix Configuration - Resource Co
Page 42 and 43: Postfix Configuration - Address Man
Page 44 and 45: Postfix Configuration - Address Man
Page 47 and 48: ACCESS(5) ACCESS(5) Page 1 of 3 NAM
Page 49: 1 Page 3 of 3 http://www.porcupine.
Page 52 and 53: ited to regular files. For example,
Page 54 and 55:
BOUNCE(8) BOUNCE(8) Page 1 of 2 NAM
Page 56 and 57:
CANONICAL(5) CANONICAL(5) Page 1 of
Page 58 and 59:
canonical_maps List of canonical ma
Page 60 and 61:
CONFIGURATION PARAMETERS The follow
Page 62 and 63:
BOUNCE(8) BOUNCE(8) Page 1 of 2 NAM
Page 64 and 65:
FLUSH(8) FLUSH(8) Page 1 of 3 NAME
Page 66 and 67:
fast_flush_purge_time Remove an emp
Page 68 and 69:
Problems and transactions are logge
Page 70 and 71:
parameter. Page 4 of 5 Timeout cont
Page 72 and 73:
LOCAL(8) LOCAL(8) Page 1 of 7 NAME
Page 74 and 75:
estricts delivery to external comma
Page 76 and 77:
details and for default values. Use
Page 78 and 79:
that is written to upon delivery).
Page 80 and 81:
Page 2 of 3 SIGTERM Upon receipt of
Page 82 and 83:
PCRE_TABLE(5) PCRE_TABLE(5) Page 1
Page 84 and 85:
PICKUP(8) PICKUP(8) Page 1 of 2 NAM
Page 86 and 87:
PIPE(8) PIPE(8) Page 1 of 5 NAME pi
Page 88 and 89:
This macro expands to the extension
Page 90 and 91:
ounce(8) non-delivery status report
Page 92 and 93:
-r When updating a table, do not wa
Page 94 and 95:
POSTCAT(1) POSTCAT(1) Page 1 of 1 N
Page 96 and 97:
POSTDROP(1) POSTDROP(1) Page 1 of 2
Page 98 and 99:
POSTFIX(1) POSTFIX(1) Page 1 of 2 N
Page 100 and 101:
POSTKICK(1) POSTKICK(1) Page 1 of 2
Page 102 and 103:
POSTLOCK(1) POSTLOCK(1) Page 1 of 2
Page 104 and 105:
POSTLOG(1) POSTLOG(1) Page 1 of 1 N
Page 106 and 107:
default, postmap creates a new data
Page 108 and 109:
POSTSUPER(1) POSTSUPER(1) Page 1 of
Page 110 and 111:
LICENSE The Secure Mailer license m
Page 112 and 113:
The queue manager implements a vari
Page 114 and 115:
This parameter also limits the size
Page 116 and 117:
REGEXP_TABLE(5) REGEXP_TABLE(5) Pag
Page 118 and 119:
RELOCATED(5) RELOCATED(5) Page 1 of
Page 120 and 121:
Yorktown Heights, NY 10598, USA Pag
Page 122 and 123:
Page 2 of 5 -C config_file (ignored
Page 124 and 125:
Page 4 of 5 DIAGNOSTICS Problems ar
Page 126 and 127:
SHOWQ(8) SHOWQ(8) Page 1 of 1 NAME
Page 128 and 129:
command after a configuration chang
Page 130 and 131:
Page 4 of 4 smtp_helo_timeout Timeo
Page 132 and 133:
Support older Microsoft clients tha
Page 134 and 135:
Page 4 of 5 smtpd_hard_error_limit
Page 136 and 137:
SPAWN(8) SPAWN(8) Page 1 of 2 NAME
Page 138 and 139:
TRANSPORT(5) TRANSPORT(5) Page 1 of
Page 140 and 141:
the entire domain being looked up.
Page 142 and 143:
details and for default values. Use
Page 144 and 145:
VIRTUAL(5) VIRTUAL(5) Page 1 of 4 N
Page 146 and 147:
site is equal to $myorigin, when si
Page 148 and 149:
VIRTUAL(8) VIRTUAL(8) Page 1 of 4 N
Page 150 and 151:
Specifies a minimum uid that will b
show all

Postfix Overview - Introduction - SCN Research

Create successful ePaper yourself

Delete template?

Save as template?