You may have seen an message in your server logs that stated "Recipient address rejected: greylisted by CYREN IP reputation" this is part of our multi layered approach to fighting spam is to use a technique called Greylisting where we "temporarily reject" any email to a subscriber from a sender that our system has not seen before.
If the email is legitimate their server will retry in just a few minutes and this time it will be accepted. And from then on out, any message to you from them will come in at full speed. It's just the first time that you'll notice a delay.
The major ISP's have been whitelisted in our Greylisting databases, but their mail is still subject to spam and virus filtering.
The Pro's of Greylisting
Spammers rely on sheer volume for their business model to work, they don't hold or queue messages on their servers hoping that they will be accepted in just a few minutes. They fire and forget. Their software is built to send as many messages in the shortest amount of time possible and they don't play by the tules.
The rules in this case is that most mail servers after getting a temporary failure will retry their message again in 15 minutes from the first time that they sent it. Our mail servers see this second attempt as a signal that the mail is legitimate and then we create an association in your account for this particular sending - sending messages to your account. Every subsequent message will come through at full speed, but it's the first time that you may see a delay.
The biggest disadvantage of greylisting is that for unrecognized servers, it destroys the near-instantaneous nature of email that users have come to expect. Mail from unrecognized servers is typically delayed by about 15 minutes, and could be delayed up to a few days. A customer of a greylisting ISP can not always rely on getting every email in a pre-determined amount of time. The biggest impact that we see is for password reset emails, shopping cart and subscription confirmations. Just realize that these can take a few minutes more than they used to.
We will be implementing a process where you will be able to whitelist email domains so that they are not subject to the filtering.