message, and injects the message into the queues for those channels. Depending on configuration, submit may then call deliver, or deliver may run later as part of periodic processing. Deliver does no direct processing of messages; instead it invokes outbound (delivery) channels, tells them which messages to process, and gives them a list of recipient addresses for each message. Each outbound channel delivers the message to those recipients who are to be reached by that channel, and reports to deliver which addresses were successfully delivered to. Deliver then updates the queues to mark the addresses that were delivered to, removes the message from any queues that have been completely processed, and if all queues have been processed removes the message text itself. Configuration MMDF approaches administrative configuration differently than other popular MTAs. In the choice between placing specialized knowledge into the software, versus requiring that it be created through administrator's configuration instructions, MMDF chose the former. Hence, arbitrary header rewriting is performed by hard-coded software, with configuration limited to choices among existing rewriting alternatives. This makes configuration simpler and safer for administrators, who use simple key-value textual tables. It also takes more effort to create a new rewriting choice, but that effort needs to occur only one time, by a single technical expert. The main types of tables are domain, channel, and alias tables. Domain tables are used for domain name canonicalization. Channel tables select the outbound channel on the basis of the next-hop domain name, and also encode per-domain-name parameters for the particular channel, such as the UUCP node name or IP address. Alias tables set up both simple aliases and mailing lists. DNS can be and usually is used for these purposes as well, in the form of "DNS tables" that have the same key-value form. The meaning and effect of entries in these tables are more obvious than the configuration data of more generalized MTAs, but their restricted form also limits the effects that can be produced. Market share By the end of 2006, MMDF had a market share well behind other mailers such as sendmail, postfix, qmail, exim, and Microsoft Exchange. MMDF is considered legacy software. References External links MMDF Users Group MMDF FAQ Message transfer agents