Greylisting is a method of defending e-mail users against spam. A mail transfer agent (MTA) using greylisting will "temporarily reject" any email from an unrecognized sender. If the email message is legitimate, the originating SMTP Server will resend using "Message Retry Interval" configuration, and the email message will be accepted this time.
The "Message Retry Interval" is configurable and is configured in the originating SMTP server.
Please Follow the steps below to configure Greylisting for the recipient domains.
Login to the iSheriff Cloud Console.
Navigate to Filter Management à E-mail Filter à Setup à Recipient Domains
Select Enable/Disable from the dropdown menu for the each domain as needed. Note: The Greylisting feature is disabled by default.
The Impact on Mail Flow:
The Greylisting, by its nature, can introduce delays in initial message flow, but these delays are generally brief and non-recurring for a given recipient-sender combination. The length of the delay is dependent on how long a sending mail server waits before retrying after the initial deferral of the message. While a few sending mail servers - typically those used for high-volume mailings - will have a relatively long retry interval, most mail servers will automatically resend a temporarily deferred message in 15 minutes or less. Additionally, since the email “relationship” (sender IP address, sender address, and recipient address) is whitelisted after a single temporary deferral, there should not be any subsequent delays after that initial message.