What is Mail Relaying?
General overview of mail relaying and how to configure MailSite.
MailServers including MailSite will by default accept email for addresses that are hosted locally (see NOTE 1 below for the exception to this). For example if you have ‘email.com’ as a domain within MailSite and have the mailbox ‘test’, then MailSite will accept email for email@example.com from any user, regardless of their IP address.
If a sender tries to send to a non-local domain via MailSite, such as Hotmail.com or Yahoo.com then this is considered relaying. Such transactions should require some authentication mechanism to prevent abuse. If there is no such requirement, then a spammer can use your system to relay email with no bounds.
To keep MailSite secure from abuse from spammers, you should select the option ‘Require SMTP authentication for relaying’ within the MailSite Console under Security Properties > SMTP. If you have a specific set of IP addresses which are trusted, you can permit relay from those IP’s without the need to authenticate. To do this, select the box ‘Friendly hosts are exempt from this requirement’. Then take the IP range or subnet and enter within ‘Accept mail for relay from these Friendly hosts’ (or within the Friendly Subnets, whichever is applicable). Anyone sending from an IP in that range will be able to relay through the server without the need to authenticate.
For the majority of customers you should ensure that within ‘accept mail for relay to these domains’ and ‘accept mail for relay from these friendly hosts’ that the * (asterisk) character is NOT present. The * acts as a wildcard. Having this in either of those options will potentially leave your system as an open relay.
For clients connecting via webmail, it automatically authenticates when sending.
NOTE 1: The exception to this is if the option ‘require SMTP authentication for local mail delivery’ is enabled then the sender will need to authenticate when sending to local users. This configuration is commonly used when a gateway server is in front of MailSite
See these other knowledge base documents:
Last revised 2010-7-14