Is there any way to disable spam filter completely?

Still there is no information from Microsoft about the Spam Filter, specifically on the option to disable the filter.

Well, it has only been 4+ years since this thread was started, perhaps they need a little more time?

In relation to my last post I would like to add the following. Maybe there is a good reason for MS not to allow us to disable the filter. If too many users do not delete their emails on MS servers (e.g. setting the email client to delete received messages after a certain amount of days), then a large number of spam emails would stay indefinitely on the servers. This could pose a problem of storage capacity: a problem that increases (a) as spam increases, and (b) as email users are less careful in cleaning their inboxes.

I feel a little foolish offering an explication that MS could (should?) present themselves. But, well, that is a possible logical explanation, and only MS knows if the numbers are such as to make it true.

I think you are being excessively generous to MS here.  The above is nothing they can't mitigate with a simple quota facility.  There really is no logical reason why they shouldn't allow users more control over this behaviour.

However my feeling is that the filter is getting smarter. Meaning that apparently less messages are wrongly classified as Spam.

Yes, but it is still unreliable so you can miss email notification. I use the Outlook.com email just for forwarding emails from my own mail server, to flatten deep IMAP folders hiearchy into single Inbox for primitive mobile devices. I setup sending another notification message (with fixed From address explicitely enabled in the buggy spam filter) on my server so typically I forward two emails to Outlook.com account upon one incoming message. That way I receive the original message (if not detected as spam) and always the second notification message. This is currently the only option to not miss notification of every new email.

But I agree the number of wrongly classified messages is going down last two weeks.

Still there is no information from Microsoft about the Spam Filter, specifically on the option to disable the filter.

However my feeling is that the filter is getting smarter. Meaning that apparently less messages are wrongly classified as Spam.

In relation to my last post I would like to add the following. Maybe there is a good reason for MS not to allow us to disable the filter. If too many users do not delete their emails on MS servers (e.g. setting the email client to delete received messages after a certain amount of days), then a large number of spam emails would stay indefinitely on the servers. This could pose a problem of storage capacity: a problem that increases (a) as spam increases, and (b) as email users are less careful in cleaning their inboxes.

I feel a little foolish offering an explication that MS could (should?) present themselves. But, well, that is a possible logical explanation, and only MS knows if the numbers are such as to make it true.

I created the diagnostic report of message rules and found the implementation is simple, the generated InboxRules.txt file reveals a hidden rule that is always processed as the first one (ExecutionSequence="0"):

<Folder

  FolderName="Doručená pošta"    <--- Inbox

  Rules="1">

  <Rule

    Index="0"

    Name="Junk E-mail Rule"

    Provider="JunkEmailRule"

    ExecutionSequence="0"

    Level="0"

    StateFlags="Enabled, ExitAfterExecution, SkipIfSCLIsSafe"

...

                       <Restriction

                          Type="Exist"

                          PropTag="SpamConfidenceLevel / 40760003" />

                        <Restriction

                          Type="Property"

                          Operation="GreaterThan"

                          PropTag="SpamConfidenceLevel / 40760003"

                          MultiValued="False">

                          <Property

                            Id="SpamConfidenceLevel / 40760003"

                            DataType="Int / 00000003">

                            <Value>-1</Value>

                          </Property>

                        </Restriction>

...

      <Action

        Type="OP_MOVE"

        UserFlags="00000000"

        FolderName="Nevyžádaná pošta">      <--- Junk

If Microsoft allowed us either to disable the hidden rule or move it down, the issue would be resolved.