Client Restrictions

This section allows high-level, general policies of Client Restrictions to be configured. The Client Restrictions define a first cut at what clients may connect to the mail server on this machine. Fine tuning of these restrictions will be discussed later in section . Depending on the setting here the mail server will determine if the user's e-mail can be sent, relayed or rejected.

These helps prevent unknown machines and possibly spam from being sent through the server.

None

Selecting None removes all client restrictions. All connecting mail servers will be able to send mail to this server if the destination is valid for this server. This option should be avoided.

Moderate

Selecting Moderate rejects mail if either the sender domain or the recipient domain is not a FQDN (Fully Qualified Domain Name) or cannot be resolved by DNS. It will also reject mail if the sender hostname is in invalid format. This is the recommended setting.

Strict

Selecting Strict sets the mail server to reject any incoming mail where the sender's hostname can't be resolved by DNS, in additions to all other restrictions at the moderate level. This option may cause some legitimate mail to be rejected.