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| Home > Services & Help > Spam and SpamAssassin > Greylisting | |||
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FAQ for Greylisting |
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Welcome to The WELL! Here are the answers to some questions about Greylisting. Questions:What is Greylisting?
Answers: What is Greylisting Greylisting is an anti-spam technique that introduces a short delay before accepting mail. When a message with a given "tuple" (see next question for definition) arrives, greylisting initially refuses to accept the message, failing with a temporary rejection code. If that same "tuple" is seen again after a suitable delay, the mail is then accepted. What is "tuple"? Every message that arrives comes from a specific server (identified by an IP number), and has a specific sender address, and a recipient address. These 3 pieces of information - the IP, the sender, and the recipient - comprise a tuple. The greylisting software uses this tuple to determine whether it should issue a temporary reject code or accept the message. How does this stop spam? Legitimate mail servers respond to a temporary rejection code by simply queueing the rejected message for later delivery. Such servers will attempt to deliver the message again at some time in the near future - typically after a delay of 5 minutes to an hour, but the interval can be shorter or longer depending on how the delivering server is configured. Some spam servers also work this way, but many do not - many spam servers don't bother to check whether delivery was accepted, so mail blocked with a temporary rejection code is simply never delivered. What kind of results can I expect? The actual amount of spam reduction you can expect to see depends a great deal on how much spam you receive, and where that spam comes from. Our tests show a wide range of results with some people experiencing only minor reductions in the amount of spam received, and others experiencing major reductions. Will Greylisting delay my legitimate email? Yes, it will. When mail with a given tuple arrives, the greylisting software checks its database to see if that tuple has been seen recently. There are 3 possible situations: 1. The tuple has not been seen at any time in the past 7 days. In this case, the mail is temporarily rejected, and a 10 minute countdown timer for this tuple is started. 2. The tuple was first seen less than 10 minutes ago. In this case, the mail is temporarily rejected again, but the 10 minute countdown timer is allowed to keep ticking. 3. The tuple was first seen more than 10 minutes ago, but less than 7 days ago. The mail is accepted. Each time a message with the same tuple is seen thereafter, the 7 day countdown restarts. How long will Greylisting delay my email? At least 10 minutes for tuples that aren't currently in the 7 day "whitelisting" period that starts after a message is accept. In most cases, mail will be delivered within an hour, but depending on how the sending server is configured, it could be much longer. Can I whitelist certain tuples, senders or IP addresses? Not under normal conditions - greylisting is intended to be a low-maintenance low-resource anti-spam technique, and user configurable whitelisting would tend to be at cross-purposes with that. Will greylisting affect email that I send out? Mail that you send will not generally be subject to greylisting. Caveat: There is one situation where you might run into greylisting while trying to send mail - most people will never encounter this, but it can happen: if you are sending mail to the @well.com address of someone who is using greylisting, and your POP client is using smtp.well.com to send the mail, then you might encounter a greylisting-related error. Typically, the error will say something about greylisting being in effect, and a suggestion that you try again later - however, the exact message you see depends on your email client. If you do encounter a greylisting-related error while sending mail to an @well.com address, there are three workarounds: - Have your POP client check for new mail on mail.well.com (or mh.well.com), then try resending the mail a few seconds later. Your outgoing mail won't have to deal with greylisting if you check for mail no more than 30 minutes prior to sending. Note that this is the same "POP before SMTP" authentication method required when sending mail to non-WELL addresses:
- Wait 10 minutes and try again. Many POP clients will re-send
automatically the next time you send any mail, but it's up to you
to check that the message did indeed get sent.
- Send the mail through another SMTP server (such as your ISP's). How do I turn on Greylisting? - Go to: https://www.well.com/utils
- Select the Spam option
- Greylisting can be turned on in the Greylisting section near the bottom of the page. You can also request a
nightly report about how greylisting is working for you.
- Click the Update button For information about The WELL or for WELL Customer Support, contact: WELL Help Desk
email: helpdesk@well.com for
more information about The WELL and WELL Customer Support. |
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