Smarthost

Setting up a smarthost

We run most of our own network services – inbound and outbound email, DNS and web presence. We run separate services for inbound and outbound email to give us more flexibility in how we set things up.

Open Relays and Mail Sinks

Email is a “store and forward” protocol. The sender doesn’t connect directly to the recipient to send the mail with just one network hop, rather the sender connects to a mailserver (usually referred to as an “MTA”, short for Mail Transfer Agent) and sends the message there. Once that MTA has received the message it sends it on to another MTA, and so on until it reaches the recipient.
Mail clients typically don’t have any intelligence built in to them to decide which MTA to send an email to. Instead they’re configured to blindly send every message to one particular local MTA, the smarthost, which then does all the proper SMTP work to decide where to send it on to.

I need IP addresses to handle the volume

Number two of seven in our occasional series on why ESPs need, or don’t need, lots of IP addresses to send mail properly.