Servage.net, my current host who I reviewed last week have just introduced a new anti-spam system. Whilst this is a welcome addition, there are a few issues to be aware of…
One criticism in my review here was that Servage only had a very basic validation system to help prevent spam. On my main email address in use for many years I receive a large amount of spam a fair portion of which I never want even the title actually downloaded into my mail client. I’m not happy with the verification system because I can’t customise the auto-reply it sends, but I don’t want my Inbox filling up with crap either.
Servage have now introduced a new system which has cut 99.9% of the spam I receive – a damn impressive figure for any anti-spam system. However, there is a “but” because Servage are using Grey-Listing.
For those who don’t know grey-listing involves the server on the receiving end of the transaction refusing the first attempt to deliver an email unless it knows it to be from a good sender. Most proper email servers will queue the email and try again after a certain amount of time. A lot of spam nets (mostly zombie home PCs) don’t implement a queue and therefore don’t try multiple times, so the email is never accepted.
Great yes? Not a stock or granny sex email in sight! However, the problem comes in when considering the delays this can cause. I sent a test message to my account from work at 11/03/07 11:18 – because of the Grey-Listing and what look like a couple of mail server problems on servage’s part the email wasn’t accepted by their server until 20:27:48
Not a major problem, but if you work in IT how many business people have you run into who haven’t the foggiest idea that email isn’t necessarily instant?
Depending on how Servage have their system setup the successful transaction should persist to prevent Grey Listing of my work email address – however this may expire after a set period without an email transaction leading to another large delay the next time. It would be useful if they gave some idea of what the figure was.
Grey Listing has a fair few interesting implications for server admins as it adds to the amount of email sitting in queues rather than being delivered immediately (currently a very high percentage of email is delivered immediately and some MTAs such as Exim aren’t great at dealing with large queues). The lessons is that pretty much any anti spam solution has its downsides for server admins
- Spam Assassin = Server Load
- Grey Listing = More email on the queue
- Sender Verification callouts = Not all servers reply correctly or at all, potential for DOS
There is also the “soft” implication of having to explain any delay via helpdesk to users.
Which just goes to show, you just can’t have everything 
…
Or more accurately you can have somewhat delayed email and thankfully lose the “finicky grandmother” communications.
