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📛 NAME

generic - Postfix generic table format

🚀 Quick Reference

Use Case	Command	Description
🏠 Local to Internet	smtp_generic_maps = hash:/etc/postfix/generic	Transform local addresses to Internet addresses for outgoing SMTP mail
🏗️ Build Indexed Map	postmap /etc/postfix/generic	Rebuild the indexed database file after editing the text file
🔍 Query Map	postmap -q "user@domain" /etc/postfix/generic	Test the mapping for a specific address
📝 Query from stdin	postmap -q - /etc/postfix/generic < inputfile	Bulk query the mapping using stdin

📖 SYNOPSIS

postmap /etc/postfix/generic

postmap -q "string" /etc/postfix/generic

postmap -q - /etc/postfix/generic <inputfile

📝 DESCRIPTION

The optional generic(5) table specifies a 📇 address mapping that applies when mail is delivered. This is the 🔄 opposite of canonical(5) mapping, which applies when mail is received.

Typically, one would use the generic(5) table on a system that 🌐 does not have a valid Internet domain name and that uses something like 🏠 localdomain.local instead. The generic(5) table is then used by the 📧 smtp(8) client to 🔄 transform local mail addresses into valid Internet mail addresses when mail has to be sent across the Internet. See the 💡 EXAMPLE section at the end of this document.

The generic(5) mapping affects both 📨 message header addresses (i.e. addresses that appear inside messages) and ✉️ message envelope addresses (for example, the addresses that are used in SMTP protocol commands).

Normally, the generic(5) table is specified as a 📄 text file that serves as input to the ⚙️ postmap(1) command. The result, an 🗂️ indexed file in dbm or db format, is used for fast searching by the mail system. Execute the command "postmap /etc/postfix/generic" to rebuild an indexed file after changing the corresponding text file.

When the table is provided via other means such as 🗃️ NIS, LDAP or SQL, the same lookups are done as for ordinary indexed files.

Alternatively, the table can be provided as a 🧩 regular-expression map where patterns are given as regular expressions, or lookups can be directed to 🌐 TCP-based server. In those case, the lookups are done in a slightly different way as described below under "REGULAR EXPRESSION TABLES" or "TCP-BASED TABLES".

🔤 CASE FOLDING

The search string is folded to lowercase before database lookup. As of Postfix 2.3, the search string is not case folded with database types such as regexp: or pcre: whose lookup fields can match both upper and lower case.

📄 TABLE FORMAT

The input format for the postmap(1) command is as follows:

• pattern result — When pattern matches a mail address, replace it by the corresponding result.
• blank lines and comments — Empty lines and whitespace-only lines are ignored, as are lines whose first non-whitespace character is a `#`.
• multi-line text — A logical line starts with non-whitespace text. A line that starts with whitespace continues a logical line.

🔍 TABLE SEARCH ORDER

With lookups from indexed files such as DB or DBM, or from networked tables such as NIS, LDAP or SQL, each user@domain query produces a sequence of query patterns as described below.

Each query pattern is sent to each specified lookup table before trying the next query pattern, until a match is found.

• user@domain address — Replace user@domain by address. This form has the highest precedence.
• user address — Replace user@site by address when site is equal to $myorigin, when site is listed in $mydestination, or when it is listed in $inet_interfaces or $proxy_interfaces.
• @domain address — Replace other addresses in domain by address. This form has the lowest precedence.

✍️ RESULT ADDRESS REWRITING

The lookup result is subject to address rewriting:

• When the result has the form @otherdomain, the result becomes the same user in otherdomain.
• When "append_at_myorigin=yes", append "@$myorigin" to addresses without "@domain".
• When "append_dot_mydomain=yes", append ".$mydomain" to addresses without ".domain".

🔗 ADDRESS EXTENSION

When a mail address localpart contains the optional recipient delimiter (e.g., user+foo@domain), the lookup order becomes: user+foo@domain, user@domain, user+foo, user, and @domain.

The propagate_unmatched_extensions parameter controls whether an unmatched address extension (+foo) is propagated to the result of table lookup.

🧩 REGULAR EXPRESSION TABLES

This section describes how the table lookups change when the table is given in the form of regular expressions. For a description of regular expression lookup table syntax, see regexp_table(5) or pcre_table(5).

Each pattern is a regular expression that is applied to the entire address being looked up. Thus, user@domain mail addresses are not broken up into their user and @domain constituent parts, nor is user+foo broken up into user and foo.

Patterns are applied in the order as specified in the table, until a pattern is found that matches the search string.

Results are the same as with indexed file lookups, with the additional feature that parenthesized substrings from the pattern can be interpolated as $1, $2 and so on.

🌐 TCP-BASED TABLES

This section describes how the table lookups change when lookups are directed to a TCP-based server. For a description of the TCP client/server lookup protocol, see tcp_table(5). This feature is not available up to and including Postfix version 2.4.

Each lookup operation uses the entire address once. Thus, user@domain mail addresses are not broken up into their user and @domain constituent parts, nor is user+foo broken up into user and foo.

Results are the same as with indexed file lookups.

💡 EXAMPLE

The following shows a generic mapping with an indexed file. When mail is sent to a remote host via SMTP, this replaces his@localdomain.local by his ISP mail address, replaces her@localdomain.local by her ISP mail address, and replaces other local addresses by his ISP account, with an address extension of +local (this example assumes that the ISP supports "+" style address extensions).

/etc/postfix/main.cf:

smtp_generic_maps = hash:/etc/postfix/generic

/etc/postfix/generic:

his@localdomain.local   hisaccount@hisisp.example
her@localdomain.local   heraccount@herisp.example
@localdomain.local      hisaccount+local@hisisp.example

Execute the command "postmap /etc/postfix/generic" whenever the table is changed. Instead of hash, some systems use dbm database files. To find out what tables your system supports use the command "postconf -m".

🐛 BUGS

The table format does not understand quoting conventions.

⚙️ CONFIGURATION PARAMETERS

The following main.cf parameters are especially relevant. The text below provides only a parameter summary. See postconf(5) for more details including examples.

• smtp_generic_maps — 📇 Address mapping lookup table for envelope and header sender and recipient addresses while delivering mail via SMTP.
• propagate_unmatched_extensions — 🔗 A list of address rewriting or forwarding mechanisms that propagate an address extension from the original address to the result. Specify zero or more of canonical, virtual, alias, forward, include, or generic.

Other parameters of interest:

• inet_interfaces — 🌐 The network interface addresses that this system receives mail on. You need to stop and start Postfix when this parameter changes.
• proxy_interfaces — 🌐 Other interfaces that this machine receives mail on by way of a proxy agent or network address translator.
• mydestination — 🏠 List of domains that this mail system considers local.
• myorigin — ✍️ The domain that is appended to locally-posted mail.
• owner_request_special — 👤 Give special treatment to owner-xxx and xxx-request addresses.

📚 SEE ALSO

• postmap(1), Postfix lookup table manager
• postconf(5), configuration parameters
• smtp(8), Postfix SMTP client

📄 README FILES

Use "postconf readme_directory" or "postconf html_directory" to locate this information.

• ADDRESS_REWRITING_README, address rewriting guide
• DATABASE_README, Postfix lookup table overview
• STANDARD_CONFIGURATION_README, configuration examples

📜 LICENSE

The Secure Mailer license must be distributed with this software.

📜 HISTORY

A genericstable feature appears in the Sendmail MTA.

This feature is available in Postfix 2.2 and later.

👤 AUTHOR(S)

Wietse Venema

IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA

Wietse Venema

Google, Inc.
111 8th Avenue
New York, NY 10011, USA

📛 NAME 🚀 Quick Reference 📖 SYNOPSIS 📝 DESCRIPTION 🔤 CASE FOLDING 📄 TABLE FORMAT 🔍 TABLE SEARCH ORDER ✍️ RESULT ADDRESS REWRITING 🔗 ADDRESS EXTENSION 🧩 REGULAR EXPRESSION TABLES 🌐 TCP-BASED TABLES 💡 EXAMPLE 🐛 BUGS ⚙️ CONFIGURATION PARAMETERS 📚 SEE ALSO 📄 README FILES 📜 LICENSE 📜 HISTORY 👤 AUTHOR(S)