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An Interesting Kerio Problem

I went to see a Kerio customer this morning. This isn't my direct customer; the installation was actually done by their ordinary computer support folks, and I normally deal with them. However, the customer has been complaining about performance and spam, so I went on-site to check on it.

I found that they were using Outlook and Outlook Express clients, all set to POP. That's not what I had recommended - for one thing, it means users have no access to the Junk Mail folder where Kerio puts Spam and it also means that Kerio can't learn about spam - if they were running Imap, dragging a message to Junk Mail helps train the spam engine. So not only can't the server learn about Spam, but they need to set the Spam threshold higher than normal to avoid false positives that they have no convenient way to retrieve.

But that wasn't the worst of it. Each users account was set up to leave a copy of each message on the server. That's good - it means that if you access from outside by Webmail or an iPhone or other device, you'll see a consistent view of your folders. However, they had not checked either of the deletion options (delete from server after so many days or delete after the message is locally purged). That means that every single message ever received is still on the server!

That will definitely impact performance. It's fairly easy to fix - see Fixing Large Kerio Mailboxes - so I have sent their support folks full instructions for doing that. I've also suggested that they at least consider using Imap or Webmail to get better control of spam

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© Anthony Lawrence

Mon Oct 12 17:26:37 2009: 7199   TonyLawrence

If they had reasonably current Outlook, I could recommend the Kerio Outlook Connector, though as they have zero interest in calendars, scheduling or public folders, that doesn't really offer anything over IMAP.

If they do insist upon staying with POP, they could remove the Kerio rule that puts Spam into Junk Mail, and then write an Outlook rule that moves messages marked "** SPAM" into another local folder. That would need to be done at each user.

Mon Oct 12 18:13:57 2009: 7200   MikeHostetler

Never deleting spam? Wow!

It's amazing how many problems come down to disk space, too much data, etc.

What scheme does Kerio use for Spam? Bayesian filters? I like a combination of that and graylisting, although graylisting can really confuse the sender if their mail server is poorly configured.

Mon Oct 12 18:19:57 2009: 7201   TonyLawrence

Kerio uses a variety of methods, including Bayesian, user rules, RBLS's and more. See


Mon Oct 12 18:21:31 2009: 7202   TonyLawrence

Oh, and not simply not deleting Spam - not deleting ANYTHING, ever.

Which is fine if you move stuff to other places - not fine to leave it in the Inbox!

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