MailEnable Enterprise Guide
SMTP - Greylisting

Greylisting is configured under the SMTP options and works by initially delaying an incoming email from a particular IP address. Since mail servers would normally retry sending a message, when the message is attempted to be sent after this initial delay period it will be accepted. Spammers rarely retry messages, and therefore will be blocked. If a spammer does retry a message, hopefully within that time the IP address of the sender has been reported to a DNS blacklist that is in use, and can still be blocked.

Greylisting can be enabled for the SMTP service and the message retry initial delay time and the time the IP and sender/recipient is remembered for can be configured here.



Enable greylisting  

Enables SMTP greylisting.

Greylisting enabled for all users:

Enables SMTP greylisting for all mailboxes

Greylisting status determined by postoffice:

Will set the greylisting option to be determined by the postoffice. Please see Postoffice - Feature Selection for more information.

Messages must be retried this many minutes after initial delay

When the SMTP service accepts a connection from an IP address it will remember the sender and recipient and the connection will be temporarily refused. The connection will be refused until after this initial delay period.

Senders will be remembered for

After a sender has sent the message the second time, the sender, recipient and sender IP address are remembered for this time period, to prevent the email being delayed again.

Sensitivity for greylisting IP matching By default an exact IP address is required for an incoming message to pass through. You can loosen this restriction by changing the mask matching that is done on the IP address.
Allow IP and domain exceptions to the greylisting Some servers do not work well with greylisting. For example, Gmail may try to send the same message from different IP addresses. By adding their IP addresses you are able to allow Gmail to bypass greylisting checks. If the domain has an SPF record you are able to enter the domain instead of the IP addresses. The SMTP service will then check to see if the IP address matches the SPF record of the domain in order to determine whether to bypass greylisting.

When a client or server is being delayed due to greylisting, they will receive the following SMTP message:

452 This server employs greylisting as a means of reducing spam. Please resend e-mail shortly.



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