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Mail Relay Demon Email Back-up service for SMTP customers Demon SMTP mail relays function as a secondary MX service, backing up your email for up to 8 days in the event of your primary MX server failing or going offline. From June 2007, we will be making it harder for spam to get into the backup server by rejecting any individual email if Spamhaus, DCC or our proprietary techniques consider it to be spam, bulk or excessively large mail. Greylisting and Recipient Verification techniques will defer suspicious mail. In non-fault circumstances the SMTP mail feed connects directly to your network without filtering. The filtering described on this page is only applied to the mail that we back up if your mailserver has an outage. Who gets this service?
How we will reduce spam and bulk mail These measures are not intended to affect mail coming from senders using their ISP's outbound mail facility. For mail to be backed up during a customer's mail server outage senders Mail Transfer Agent (MTA) must say HELO/EHLO and use RFC 2821 addresses in MAIL FROM/RCPT TO, not 822 addresses.
Greylisting Greylisting defers mail from an IP address, sender and recipient combination which we've not previously seen, expecting any normal mail service to retry to achieve success. Once successfully passed Greylisting, the combination will be allowed to send further mail without any delay. Spammers using throwaway domains There's also a change to our DNS resolution, we only cache DNS for 5 minutes - to help stop spammers using throwaway domains (see FAQ 2). Recipient Verification We will treat email going to verified email addresses differently from email going to other addresses. The Demon Backup service will build up a list of valid email addresses for a given customer domain. If the customer never accepts mail from the Demon Backup service then either the customer is not running a mail server or has a firewall set up that blocks traffic we have backed up. If this happens, the Demon Backup service will defer all of the customer's mail. Newly registered domains or newly transferred domains will require time to verify valid recipient addresses. This may mean if there is an outage on the customer line while the domain is new to us, the Demon backup service will defer mail rather than act as a backup. We can reassure customers that during this temporary "learning" period the sender will be invited to try again later, rather than get a permanent rejection of the mail. Frequently Asked Questions
What's the difference between "Deferred" and "Rejected" email? If you defer a mail you return a response code in the form 4xx which tells the connecting server that you aren't accepting the mail right now but perhaps come back later; if you reject the mail you return a 5xx response code which tells the connecting server you aren't accepting the mail ever. What is a Throwaway Domain? Spammers register a domain, send spam from it, then let it expire - if the ISP doesn't suspend it first. What is DCC? Distributed Checksum Clearinghouse detects bulk mail. See http://www.rhyolite.com/anti-spam/dcc/ for more information. What is RFC2821? To find out more about RFC2821 please read our document I would like spam filtering on my primary SMTP feed to my mail server too. Consider subscribing to MailDefender, which also stops virus and phishing mail Definitions MTA - Mail Transfer Agent - software that transfers mail from one machine to another HELO - SMTP transaction command used to identify the sending machine. EHLO - Same as HELO but uses ESMTP (Extended SMTP) |
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