The delivery of some of my email messages is being delayed, why is this?

Answer by: Kristen Jourdonais, Aplus.Net Knowledge Base Support.

Aplus.Net has implemented a new service on its mail servers to help its valued customers manage the growing problem of SPAM email (unsolicited email messages). This new service is called a Greylist.

How Greylist works:

With this new feature, Aplus.Net’s mail system will not deliver any message unless it has logs of a previous attempt to send the same message, by the same server. This may cause delays when sending emails to a particular email account for the first time. You may notice that you have not received an email from a particular sender immediately after it is sent. If this is the case, please wait approximately 30 minutes and the message will be delivered. This delay is caused by an email that is being filtered by the Greylist service for the first time. After you have received one email from a user, no email from that user will be delayed again.

Here is a basic explanation of the phases that occur with the Greylist feature:

Phase 1:

When a sending mailserver opens a session with Aplus.Net’s server, Aplus.Net logs the following:

• IP address
• Sending user
• Receiving user

Phase 2: 

Aplus.Net’s system checks the log file for any records of a previous attempt to send an email message between the user and the sender. One of the following 2 scenarios will happen:

1. At least one previous attempt is found. The email is delivered immediately.
2. No previous attempt is found. At this time the email is not delivered. This when phase 3 takes place.

Phase 3:

The sending mailserver will attempt to re-deliver the email again after 15-30 minutes. When this session is opened, Aplus.Net’s mailserver checks for a previous delivery attempt and matches the “from” email address, “to” email address, and IP address. If these match, then the sender is whitelisted, and email will not be delayed again from this user.