Here's the typical pattern: MUA -> [MSA] -> MTA -> [.. more MTAs] -> LDA -> [Mailbox Store] -> MUA
Things in [brackets] may not be used, or may take altered forms in a specific configuration. Definitions: MUA - Mail User Agent. Examples: mutt, thunderbird, webmail MSA - Mail Submission Agent. This function could be built into the MUA, or built into an MTA, or it might be a separate queuing system. Most MTAs expose a submission interface that may or may not offer separate features from their MTA interface. Examples: SMTP service, pipe to /usr/lib/sendmail, pipe to msmtp, etc. MTA - Mail Transport Agent. The primary role of an MTA is to exchange mail around the internet. An MTA may be colocated with a user agent or a delivery facility such as IMAP, but it might not. Sometimes mail moves through many MTAs on its way to a destination, but this is less common than it used to me. Most mail today encounters two MTAs: one that is colocated with the sender's submission agent, and one that triggers local delivery for the recipient. LDA - Local Delivery Agent. An LDA is responsible for handling the disposition of the mail at a destination. An MTA determines that it is a final destination (based on arbitrarily complex rules, but often just a hostname list for which it's responsible). Then it hands the mail to an LDA and awaits the LDA's assertion that delivery was performed. Procmail can be used as an LDA, but there are others. An LDA might delivery to a spool file where an MUA can retrieve it, or it might deposit the mail into a message store such as an IMAP server. Mailbox Store. Not all recipients use this, of course, but many do. To answer your question finally: An MUA (such as mutt) never interacts directly with an LDA. It either retrieves messages from a mutually-agreed location (e.g. /var/mail/username) or it contacts a message store (e.g. an IMAP server). * On 25 Jan 2013, horseriver wrote: > hi: > > Would mutt call default mail delivery agent when startup? > > thanks! -- David Champion • d...@bikeshed.us
