There are two types of SMTP Servers:

1. Regular SMTP Server
2. SMTP Proxy Server

Regular SMTP Server

SMTP server is the default mechanism to accept new messages from a client. This SMTP Server accepts incoming emails and stores the message in a local repository. If the message is bound for another SMTP server, the message gets queued and is finally delivered to the destination.

This Server can be used in all 3 operating modes (Stand-alone, Spam Firewall and Hybrid).

When should you use Smtp Server?

Consider using the SMTP Server when:

• You are using Stand-alone mode. In this mode it does not require any other email server and therefore, you cannot use the SMTP Proxy Server, OR
• When you want to distribute incoming emails to more than one server. For example, domain1.com goes to MS Exchange and domain2.com goes to a QMail server, OR
• You want to provide redundancy for your primary email server.

SMTP Proxy Server

SMTP Proxy server can only be used if you have another server in your network that accepts emails. It sits in between a client and this other SMTP server. It does not have a local queue. Instead, when a client connects to send an email, the proxy server opens a TCP/IP connection to the actual server and simply watches what the client is sending. Besides watching the email, it can also modify and block the message. If the actual server goes down, so will proxy. A proxy server requires less configuration. You do not have to configure domain names and users. This is because the primary server decides which emails to accept.

This Server cannot be used in Stand-alone mode. It can only be used in Spam Firewall and Hybrid modes.

When should you use SMTP Proxy Server?

Consider using SMTP Proxy Server when:

• Local deliveries is NOT the final destination for in-bound emails. Consider the scenario where you are using Microsoft Exchange as your email server and want to filter spam.
• You are using SMTP in Firewall or Hybrid mode.
• You have users on the Internet (outside your company’s network) who want to use your email server to send their outbound messages and you want to them to authenticate before accepting their message.