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Suso implements a spam deterring technique called Greylisting and has been since 2007 with much success. It works by initially rejecting all mail from "untrusted" domains and then allowing it in after the remote mail server retries and 2 minutes have passed. In most cases, this happens quickly and the remote mail server retries on a regular basis so the delay is only a 5 to 15 minutes. However some mail servers are either too busy to respond right away or don't retry for much longer due to the design of the software they use. This is actually rare as we don't get complaints for delayed mail very often.

The reason this stops a lot of spam is because most spammers have so much spam to send out that they can't hold onto mail that they need to send in order to retry and just never retry. Some spammers do, but from what we've seen, most don't. After we first implemented Greylisting at Suso, the amount of spam on many accounts dropped by more than 75%. It is one of the techniques that allows you to enjoy a much more spam free experience on your account.

Greylisting is actually a pretty common technique on the Internet now and many companies know how to deal with it now. However they are some mail servers out there that you may receive mail from that do not handle Greylisting well or wait hours before retrying. If you are going to receive mail from these domains on a regular basis, they will eventually become trusted mail servers and will no longer be greylisted. You may also wish to contact the managers of the domain to let them know that their mail server doesn't deal with Greylisting well. This will help them not just in sending to Suso accounts, but also to any other host implementing Greylisting, which there are many.


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