This page explains how to use the Outgoing Mail service and how it can be configured correctly. For more detailed information on what each option of the Outgoing Mail settings is for, please view the Outgoing Mail page.
When a mail is sent from a mail client or WebMail that is addressed to a non-local account, the mail will enter this service. The purpose of the Outgoing Mail service is to ensure delivery of mails to external mail accounts (accounts hosted by other mail servers). The service internally consists of 2 main parts, 'Mail Delivery' and 'Queued Mails'. This allows an outbound mail to exist in the system for a period of time and also enables busy mail servers to function well under load.
When an outbound mail fails to be delivered, it will be placed back into the mail queue where it will wait for a set period of time before another attempt to deliver the mail is made. Using the options available, you can control the length of time a mail is held in the queue before it becomes classed as undeliverable and rejected. You can also control how often the service will try to deliver a mail. Other available options allow you to control how large the queue is allowed to grow, what failure messages are sent and also the content of failure messages.
There are two modes in which the Outgoing Mail service can operate: Independent Mode and Relay Mode. Independent Mode is usually the right choice for most users and is designed for stand-alone mail servers which handle the delivery of their own mail. Relay Mode is more commonly used by users who wish to route all outbound mail through another SMTP.
In this mode, the mail server will handle the delivery of all outbound mails. Delivery usually involves performing an MX lookup, then opening an SMTP connection direct to the destination mail server. However, this mode requires access to at least one DNS which will be needed for MX lookups. If you do not provide any DNSs then the mail server will attempt to automatically detect a list of DNSs from your computer, which in most cases is usually fine. However, should you experience any problems, you may need to provide the DNS information (see our Frequently Asked Questions page for more information).
In this mode, the mail server will send all outbound mails directly to another SMTP. This is usually only required by users you wish to reroute mail through a set company SMTP, an ISP SMTP or for users who do not have access to a DNS.
Static Routes allow you to change the delivery options for a particular domain, allowing you to further control the delivery of outbound mail. Each Static Route applies to a single domain and provides access to all the same delivery options as the main delivery mode. This allows all outbound mail for a particular domain to be routed through a set SMTP. It also allows the queue lifetime and resend delay options to be adjusted, allowing a particular domain to have a longer queue life if required. This is useful to large organizations which often have a mail server per department. Static Routes are also essential in configuring a backup mail server, which should usually only try to deliver the mail back to the main mail server that the mail was intended for.
See Also: Outgoing Mail.