MailChannels Cloud sends enormous volumes of email through a large and complex infrastructure that spans the globe. But recently, we began encountering a serious challenge from a relatively old and yet still commonly used anti-spam technology called “greylisting”.What is Greylisting?
According to Wikipedia, greylisting is an anti-spam technique in which the “mail transfer agent (MTA) … will ‘temporarily reject’ any email from a sender it does not recognize. If the mail is legitimate the originating server will try again after a delay, and if sufficient time has elapsed the email will be accepted.” Greylisting can be an effective defense against spam originating from simplistic botnet SMTP clients, which do not have an internal message delivery queue and cannot retry delivery if the first attempt fails (as it does when the receiving server is implementing greylisting). Legitimate email senders always … Read More »