Outlook Spam Filter

I have recently experienced a user that has been receiving email from a client perfectly fine until yesterday when the email went into the Outlook Spam folder. My client has received email from this user fine many time before.

Is there any particular reason why Outlook suddenly marked this email as spam?

I have added the email address and domain into the white list but would like to know what caused Outlook to suddenly mark the email as spam.

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Hi Kei ,

As far as i know Microsoft use an algorithm to determine if an email is spam or not. If the score of the email is over a certain level it will mark it as spam and move it into the Junk folder.

Unless you whitelist a sender i dont think it matters how many emails you receive from them, as soon as they send something that receives a high enough score its sent to the junk folder.

sfloryPresidentAuthor Commented:
Hi Mark,

Thank you for the response.

What confuses me is that in one case, the client received the email perfectly fine and using the same email, received a reply with only a few simple words that I would not think would be acknowledged as spam to add to a score.

Hi Kei,

I'm unsure of how the algorithm actually works so god only knows how it constitutes what is spam or not. For some reason it picked out something in the reply. Either that or the user made a mistake and marked it as spam by accident.

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Blue Street TechLast KnightCommented:
Hi sflory!

The reason for the change can be related to Microsoft Office Update. The Junk Mail filter algorithm is updated quite regularly. This would explain why all of a sudden it was routed to Junk Email. The other reason could be the verbiage used and/or attachment found in that particular email could have triggered it as SPAM.

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Analyzing an incoming message Outlook Junk E-mail Filter goes through the following steps:

Checks if the address is from Address Book assuming that all messages from any such address are legitimate,
Checks if the address is from GAL list that contains only addresses, from which you want to receive letters,
Checks if the address is from Safe Senders List, which is made by the user and contains the addresses trusted by the user,
Checks if the address in "To:" field of the message is from Safe Recipients List where the user keeps e-mail addresses of distribution lists or newsgroups which he/she is subscribed to,
Checks if the address is from Blocked Senders List and moves all messages with addresses from this list to Junk-Email folder,
Scans the contents of the message in order to detect spam. Spam detection filter is trying to find certain features, which are typical for spam messages, and based on this, rates the message on a scale of 1 to 100. The higher is the rating the higher is the probability that this message is spam. Afterwards the message is moved to either Inbox or Junk-Email folder depending on which anti-spam security level is chosen by the user. Being set for the High level Outlook will filter out all the letters with ratings above some quite low threshold while if the Low level is set then only highly suspicious messages with high ratings will be sent to Junk-Email folder.
Which Junk mail security level you have? You ca see it Actions->Junk E-mail->Junk E-mail Options
Blue Street TechLast KnightCommented:
@sflory: Did my answer help?
Blue Street TechLast KnightCommented:
Any updates?
Blue Street TechLast KnightCommented:
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