Definition
Greylisting is an anti-spam technique where the receiving server temporarily rejects an email with a soft bounce (typically a 4xx SMTP code), expecting a legitimate sending server to retry within a few minutes. Most spam software does not retry, so greylisting effectively blocks bulk automated spam without blocking legitimate mail.
Impact on Senders
Greylisting typically adds 5-30 minutes of delivery delay for new or unknown senders. Once a sender-server pair has been seen and verified, greylisting stops. It is common when sending from a new IP address, a new domain, or to an ISP that has not seen your sending pattern before.
Mitigation
Consistent sending patterns, proper reverse DNS (rDNS), and warm IP addresses reduce greylisting. Most established senders only experience greylisting when sending to new ISPs or after long sending pauses.
Related Glossary Terms
A/B Testing
A/B testing in email marketing is the practice of sending two variations of an email to a small sample of your list to determine which version performs better before sending the winner to the remaining subscribers.
Abandoned Cart Email
An abandoned cart email is an automated message sent to customers who added items to their online shopping cart but left without completing the purchase. It is one of the highest-converting email types in ecommerce.
AIDA Model for Email
The AIDA model (Attention, Interest, Desire, Action) is a classic copywriting framework used to structure email campaigns that guide subscribers from awareness to conversion.
AMP for Email
AMP for Email is a Google-developed framework that allows email messages to include interactive elements like forms, carousels, accordions, and live content. It turns static emails into dynamic, interactive experiences directly inside the inbox.
Anchoring Effect in Email Marketing
The anchoring effect is a cognitive bias where the first piece of information presented (the anchor) influences subsequent decisions, used in email to frame pricing and value perception.
Announcement Email
An announcement email is a dedicated campaign that communicates a specific update, milestone, or change to subscribers, from product launches and feature releases to company news and events.