Spamdyke is a spam protection program that filters incoming messages at the SMTP level by blocking connections from mail servers identified as spam sources or that match certain reverse DNS validation rules.
The Spamdyke program is enabled by default. You can enable or disable Spamdyke and configure its options from the Control Panel > Mail Manager section under the Global mail settings tab. Spamdyke can be configured only globally for the hosting account; it cannot be managed per mailbox.
Note: Messages filtered by the Spamdyke program are blocked at the SMTP level, so such blocked messages will not be delivered to your Junk Mail folder and will not be delivered if the sender is whitelisted for your hosting account or mailbox.
Spamdyke uses several methods to determine whether a sending server can be identified as a spam source:
Reverse DNS check
Messages originating from a sending mail server without valid reverse DNS record will be blocked and returned to the sender with the following error:
554 Refused. You have no reverse DNS entry.
If you receive the above message while trying to send a message through the SMTP server of your hosting account, please change the port of the outgoing server from 25 to 587.
Spamdyke can also be configured to use Graylisting. Graylisting is the technique of denying mail delivery the first time a sender tries to deliver to a recipient. The next time the remote server attempts to deliver the message, it is accepted. All future messages from the sender to the recipient are also allowed. With Graylisting enabled, our mail server will "temporarily reject" any messages from a sender it does not recognize. The originating server will try a new delivery, usually in a few minutes, and if the message is legitimate, it will be accepted. If the message is from a spammer, it will probably not be retried as spammers go through thousands of email addresses and cannot afford the time delay to retry a particular message. Standard mail servers, however, always attempt to deliver messages again if they are rejected with such a "temporary" error message, in accordance with the SMTP RFC specifications.
When a recipient/sender pair is marked as temporarily allowed, its status will remain for a given period. New messages sent within this period will refresh its duration. Once this period expires, the recipient/sender pair will undergo the Graylisting check.
Graylisting is not enabled by default, so if you wish to use it, you need to enable it through the Control Panel > Mail Manager section under the Global mail settings tab.
Information about all messages processed by Spamdyke is recorded in the mail server logs which are accessible via the Mail logs subsection of the Control Panel > Logs section.