On all our hosting plans (Ruby & Platinum), we use a greylist anti-spam system called Greylisting, to filter incoming mail and stop spam.
Greylisting is a message acceptance method that a mail server can use to block the first delivery attempt of a message and require several successful attempts from the sending mail server before allowing the original message to be relayed via the receiving mail server. This tactic is generally used to reduce spam from spammers who do not use a legitimate mail server that will retry delivery attempts to ensure they are accepted. In the case of a spam server, it will not retry sending the message.
This system is based on a principle of mail verification at the level of our receiving servers and before routing to your mailboxes (i.e. before submission).
Greylisting checks three elements: the IP address of the sending mail server (SMTP), the sender's email address (SENDER) and the recipient's address (RECIPIENT)
If this triplet is known, then the email is accepted.
If it is not, then the email is rejected and this information is added to the database of our mail systems.
The mail is in this case rejected for a minimum duration. After this interval, if the mail is resubmitted, then it will be accepted. An SMTP server complying with the standards established in the RFCs provides for resending the email over several days. This is something spam-sending robots do not do.
This allows a distinction to be made between a 'real' sending server and a 'zombie' machine, that is a corrupted machine sending spam.
To facilitate the reception of mails from the main free mail services, SafeBrands has chosen to whitelist the SMTP servers of Free, Orange, Hotmail, Yahoo and Google. This means that emails from these operators do not have to pass the Greylisting challenge.
However, if one of the servers belonging to one of the aforementioned providers is blacklisted (placed on a blacklist by an anti-spam organisation), then emails intended for you will be rejected. Indeed, Greylisting and Blacklisting are two different processes even though they are closely linked by necessity.