Both Outlook (the native Application) as OWA (outlook web access) are email clients used for MS Exchange Email server. Both support filtering emails.

I wonder if there is any difference, and if so what is the difference in which both applications employ/use/provide email filter rules (e.g. a rule to treat all emails arriving in inbox with a certain criterium (e.g. Subject email header contained certain words) in a specific way (e.g. to move it into a specific dedicated folder) )

The core difference I suspect - albeit being unable to verify on my own yet - is that the OWA filters are carried out on the server-side and are applied always, while the native application MS Office Outlook email filters are relevant only "locally".

From https://support.office.com/en-us/article/Inbox-rules-in-Outlook-Web-App-EDEA3D17-00C9-434B-B9B7-26EE8D9F5622

Each rule you create will take up space in a hidden section of your mailbox. This section is limited to 64 KB. The actual amount of space a rule uses depends on several factors, such as how long the name is and how many conditions you've applied. When you reach the 64 KB limit, you'll be warned that you can't create any more rules. If that happens, you'll have to delete or simplify some of your existing rules before you can create more. Some ways you can reduce the space used by rules are:

Is this quote an indication about the difference between the rules in OWA and Outlook Client ? At least outlook client did not tell any limits (such as the 64KB for OWA)

1 Answer 1


Basic filtering is done by Exchange for both OWA and the Outlook Client. The Outlook client can do further individual filtering but is often not required if Exchange filtering is up to date.

If regular rules are used by the client, the rules apply to the Exchange Database and then OWA and Outlook remain the same.

Clients need the same view.

  • Where did you gain that information? Is there maybe an online resource that can more detailed explain what is "basic filtering" and even how to find out what is don eby the exchange server and what by the client? That would really enrich this answer and make it more usable. Thanks for confirming implicitly that there is indeed a difference of filter/rules in between OWA and Outlook Client
    – fraleone
    Jan 6, 2020 at 14:16
  • Our clients have been using Outlook on Exchange for many years. People travelling use OWA but Outlook in Office. Spam filtering is top notch and there is no difference in what they see
    – John
    Jan 6, 2020 at 14:18
  • Glad to hear that your clients are happy. Indeed I am supprised to see "Spam filtering" mentioned in the context of those rules, since I am almost certain that this is not the usualy way spam filters are employed (since for starters Outlook email filter/rules happen once an email was already received, which most spam filtering attempts already to prevent). Anyways there must be much more to potential differences as it is said somewhere (got to add this to the question) that there is a 64k file/item that stores the OWA entered rules. thanks
    – fraleone
    Jan 6, 2020 at 14:26
  • Top notch spam filtering is done at the Exchange level, not the individual level. That is always the case when Exchange is used. Only tiny clients (no Exchange) would do it individually or by a third party spam filtering service as I use. I am not sure why you are seen only Outlook client filtering. That would be onerous for our clients when it can be (and is) automatic
    – John
    Jan 6, 2020 at 14:35
  • Is there a possibility that we are not 100% talking about the same thing? What I attempt to express using the term email filter/rules are those "rules" that go something for example like this "emails with subject [x] and from sender [y] should be moved to folder [z]". Those rules are not necessarily about spam filtering
    – fraleone
    Jan 6, 2020 at 14:39

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