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ald.net Services is pleased to offer world-class
secure IMAP email services with a full complement of anti-spam and
anti-virus filters. We also offer IMAP-based POP3 accounts.
IMAP IMAP is an email protocol that is superior to POP3. It is particularly useful for users who need to access their mail from multiple locations. For a description of IMAP, see our announcement on aldbb.ald.net, and see What is IMAP? at IMAP.org. FEATURES
What IMAP Client Should I use? We have tested several possible IMAP clients and have drawn some conclusions that we hope will help you. Please read our current recommendations. Secure web-based IMAP Services: You may access your IMAP (or IMAP-based POP3) account in a secure fashion from any internet-connected web browser using your account name and password. To use this service, visit 
at
https://imap.ald.net .
A testimonial:
Information and Discussion: For more information including pricing and our roll-out plan, visit our new bulletin board system 
at http://aldbb.ald.net .
Here are the most recent postings: Details on how it all works.Greylisting:For our first line of defense against spam and viruses we are using a relatively new technique called greylisting. You are probably familiar with "blacklisting" - often used to block mail from known spammers, and "whitelisting" - often used to unconditionally permit mail from trusted senders. Greylisting doesn't deny or accept a message on a first attempt to send it, but instead asks the sender's mail server to try again later. Most spammers and most viruses these days use a "shoot and move on" mailing procedure, and so they don't try a second time, and we don't see the spam at all. If the message is presented again anytime after the mandatory waiting period (we are using a 25 minute pause) and before the time-out period (we are using 7.5 days), the email will be checked against the xbl.spamhaus.org blacklist. If it passes, it will be accepted by our system and then examined by our antivirus program and a variety of other checks. If the mail passes those tests it is further screened by a battery of spam-detection tests which will note the results in mail headers and then placed in the recipient's mailbox. See the web page we've set up to explain why an email may have been bounced. We have the option to exempt a recipient from the antivirus and antispam filtering (but not just one or the other, currently). Auto Whitelisting: When the greylisting program accepts an email after the initial delay, it lists the combination of the sender's address, the sender's mail relay address, and the recipient's address into a whitelist database along with the current date and time. This combination will be "whitelisted" (not delayed at all) for the next seven and a half days. If the same sender sends mail through the same mail relay to the same recipient any time in the next 180 hr, it will be accepted, and the whitelist time will be reset to 7.5 days (180 hr) from that time. If no email with that combination is received during the whitelisting period, the whitelisting expires and the next email will have to go throught the initial 25 minute delay again. We also have the ability to permanently whitelist a sender domain, mail relay address, or to exempt a recipient address from the greylisting process. Blacklisting: We employ one very conservative "Exploits" blacklist (xbl.spamhaus.org) to screen mail that gets past the greylisting. This particular blacklist "is a realtime database of IP addresses of illegal 3rd party exploits, including open proxies (HTTP, socks, AnalogX, wingate, etc), worms/viruses with built-in spam engines, and other types of trojan-horse exploits." It doesn't try to block all spam, and generates few, if any, false positives. Antivirus: The antivirus system we are using is ClamAV. It checks every incoming and outgoing message that is accepted by the system (unless we have specifically exempted the sender or the recipient) for known viruses. We check for new updates four times an hour to be sure we have the most current virus definitions possible. Greylisting blocks most of the viruses, but a few still get through just from random chance. We have seen viruses that were delayed for 90 hr by the greylisting before being submitted a second time, accepted, and then quarantined by the anti-virus filter. Our antivirus filtering is no substitute for having your own antivirus software running on your computer because no antivirus system is perfect, and because email isn't the only way viruses can infect a computer. Spam Tagging: We use SpamAssassin to "tag" spam that gets past the primary blocks. SpamAssassin adds several headers to identified spam, permitting you to train your mail client to accept, classify, reroute, or delete mail based on these headers. SPF: We are using SPF (Sender Policy Framework - formerly Sender Permitted From) in two ways currently. First, we permit sites that publish valid SPF records to skip the greylisting step. Second, we use SPF results as one of the scoring criteria for SpamAssassin. We hope to begin blocking mail that says it is from us, but actually isn't, at some point in the future. Permitting this is one of the major benefits of the SPF protocol. We had tried blocking based on SPF for a short time, but found that there were too many false positives. Results: We have found the combination of greylisting and one blacklist to be far superior in blocking spam compared to the multiple blacklists that we are running on the old POP3 mail server. Greylisting, spam blocking, and antivirus filtering are optional, but are turned on by default. Check yesterday's and today's accept/reject logs to see how well these work. (Note - a virus/worm-infected file will be counted twice, once when it is first accepted, and again when it is quarantined.) Drawbacks:
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Copyright © 2004 ald.net Services, ltd.
All Rights Reserved. Information in this document is subject to change without notice. Last updated May 3, 2005 |
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