Socket Map Daemon

sockmapd

sockmapd is a socketmap server daemon for Mail Transfer Agents (MTA) that uses configurable database repositories for lookup tables.

sockmapd is written in Go Lang

Purpose

Mail Transfer Agents like Sendmail and Postfix can use either hash files, database queries, or socketmaps to lookup for valid recipients' eMail addresses, hosts or eMail addresses in blacklists or whitelists, or even header policies, just to mention a few examples.

Often we have this information stored in database servers that are not directly accessible from our DMZ where the MTAs are usually deployed. Although some MTAs (like Postifx) do support direct database access and queries, we want to keep access to our internal database well protected.

This is the case, for example, if we use dbmail, an IMAP, POP server. dbmail maintains mailboxes and their eMail aliases on the protected database server, but the MTA in the DMZ is prevented direct access to them. If we want our MTA to validate a recipient and reject, or accept the eMail for further delivery at the time it is contacted by the sender's MTA, then we need a service like sockmapd, that takes queries from the MTA and verifies whether the recipient is valid. The same applies when we want our MTA to check if a sender's eMail address or the sender MTA's host name is in our blacklist. Description

sockmapd is a configurable service daemon that accepts socketmap protocol queries (TCP protocol) on a specified TCP Port number and returns a response to the calling service client. Sockmapd queries database tables that are mapped to a service map via a configuration file that can be specified in the command line. Feature: socketmap request/response

Socketmap request queries have the format of a netstring as follows:

"[len]:[query],"

Example:

if my request is to lookup for someone@somewhere.com in the recipient map, the request string will be:

"32:recipient someone@somewhere.com,"

where 32 is the length of "recipient somebody@somewhere.com" in front of this request, sockmapd queries the database table mapped to the socketmap in the configuration file and returns a response as follows:

"9:NOTFOUND ,"

or

"24:OK someone@somewhere.com,"

The response strings are documented in the socketmap table man page.