MailEnable Enterprise Guide
Overview / Email Delivery Flow
In This Topic
    Email Delivery Flow
    In This Topic

    Sending Email

    When mail is being sent to a non-local address, this is known as “relaying” i.e. MailEnable has to "relay" the email back out.

    Requiring users to authenticate against the server prior to sending email can stop spammers from using the mail server to send email out to anyone.

    When email is being delivered to a local address, this is not relaying, and MailEnable will always accept this email. This is how email is received from other mail servers on the Internet, as they do not need to authenticate.

    Receiving Email

    When an email arrives via SMTP, the SMTP service saves this message to its inbound queue. The MTA service is constantly checking this queue for new items.  When the MTA sees the message arrive it examines the message to determine where it is to go. If the MTA service determines it is to go to a local mailbox, then it will move the message to the post office connector service outgoing queue. The post office connector will be checking its outgoing queue and can then process this message and deliver it to a users mailbox.

    The naming of the Inbound/Outgoing queues may be confusing initially. But think of the queues as always relative to the MTA service. So the MTA service will check all the inbound queues of the services and move messages to the outgoing queues of the services. Services only check their outgoing queue and if they need to create a message then they will do this in their inbound queue.

    Since the MTA service is the central service responsible for moving messages around the system, it is the logical place for all the global filters, and items such as anti-virus, Bayesian filtering, etc. (the features available are determined which version of MailEnable). Even messages arriving via SMTP and sent via SMTP are processed by the MTA service, since only the MTA can move the email from the SMTP Inbound queue to the SMTP Outgoing queue.

    Utilizing different services in this way gives MailEnable a high level of flexibility, such as allowing services to be split across machines and to permit more than one type of service to be running on different servers. But this flexibility does create one hurdle for an administrator of MailEnable, and that is the problem of being able to track a message. A message being sent to a local mailbox will be logged in the SMTP logs, the MTA logs and the post office connector logs. Fortunately there are tools and monitoring software that come with MailEnable that makes this tracking easier, but understanding the queue mechanism will make administering the MailEnable server a lot easier.