SMTP Mail Relay options

Mail relay occurs when IMail Server (or any SMTP server) accepts mail destined for another host and delivers it to that host. A message that originates on a computer other than the IMail Server host and destined for another host must pass through the IMail Server (i.e., IMail Server must relay the message). If your users (on the local network) use a POP3 or IMAP mail client to send mail via the local IMail Server, then IMail Server needs to relay mail for them. IMail Server allows for the following mail relay options (listed in order from most secure to least secure):

• No mail relay (install default)
• Relay mail for (Addresses)
• Relay mail for local hosts only
• Relay mail for local users only
• Relay mail for anyone

Local mail (destined for the IMail Server host or originating from the IMail Server host) does not use the relay function.

Note: During installation, you can select from four options: Relay for select addresses, No mail relay, Relay mail for anyone, and when upgrading: Do not change my existing local mail relay settings. After installation, you can change the relay setting in the Services tab > SMTP Settings page in IMail Server.

• No mail relay (recommended)

  The SMTP server will not accept mail destined for other hosts (any host not on the IMail Server machine) unless it comes from users who set their mail clients to do SMTP authentication. Make sure all mail clients are set up to SMTP Authenticate; otherwise, the client cannot send mail to non-local e-mail addresses. SMTP authentication means that the user name and password are presented to the mail server when the client sends a message.

• Relay mail for anyone (not recommended)

  The SMTP server accepts mail from any host that is destined for any other host, and redelivers that mail (i.e. becomes a mail gateway). This option is the least secure because it allows your server to be used by anyone to send mail to anyone. Some bulk mailers may take advantage of this capability to not only relay mail through your server, but to make it appear as if mail is originating from your server.

  If you select this option your server may be blacklisted for running an open relay. To prevent this you should select Relay mail for (Addresses).

• There are several other mail relay options available after installation including Relay mail for (Addresses), Relay for local hosts only, and Relay for local users only. No mail relay is the best option if you are unable to use Relay mail for (Addresses) because your users dial up using dynamic IP addresses.

For more information on Mail Relay options and other security features, see the IMail Administrator Help.