When OOF makes you hit EXO limits and you’re blocked from receiving emails

I recently came across something you might also run into at this time of the year or when a company wide announcement needs to be made via e-mail and the sender is in Exchange Online:

A person sent some season’s greetings, which results into being blocked by EXO as a limit was reached (you can find more about these limits here). My first thought was something like sending e.g.: 10.000 messages per day or too many recipients, but it turned out to be something different.

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Compliance bug in Exchange Online

Last week fellow MVP Vasil Michev (his very valuable blog can be found here!) stumbled across a post on Spiceworks, related to compliance feature in Exchange.

After some testing, i was able to reproduce the issue as well. As this is really a severe bug, a SevA case was opened at my companies account.

You can read and get the full details on Tony’s post here.

Note: I’ve tested this in my companies environment with the same Outlook client against Exchange 2016 CU14 and couldn’t reproduce the issue.

Once we have the root cause for this issue, you will be informed. Until then I can only recommend to open a ticket with MS.

Outlook command-line switch:”/cleanrules” (think twice!)

This post has nothing major, except a warning! I run into this some time ago and thought, this is nothing to write about.

But with the latest regression in Outlook

[INVESTIGATING] The rules on this computer do not match the rules on Microsoft Exchange

I was approached by colleagues as they lost their Outlook rules completely.

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Severe Outlook for Mac issue

Sometimes things going wrong. So this time with Outlook for Mac. Starting with version 16.22 from Insider Slow we started seen some strange behavior as suddenly additional entries in the calendar view occurred. But with version 16.23 things got even worse.

When your mailbox is in Exchange Online and you are using Outlook for Mac with this version, you should continue reading. I f not you can relax and stop reading.


There is now a new version available, which has a fix for this:

Make sure you install version 16.23.326.1!

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Why X500 addresses are so important

There are many posts and a few KB articles related to legacyExchangeDN and X500 addresses. Here some a few examples:

These are only a few examples. But there is even more: Calendar items and especially recurring meetings are highly depending on legacyExchangeDN.

In a recent M&A scenario the decision was made to perform a cleanup of X500 addresses, which definitely caused quiet a number of tickets.

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In my previous post Troubleshooting Autodiscover I wrote about Autodiscover service and the difference between POX and SOAP requests. Over the last years Microsoft evolved Autodiscover and introduced a new Autodiscover service V2. The new version is based on JSON and the main difference is the fact you don’t need to be authenticated.

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Office 365 Exchange Hybrid: When Autodiscover and legacy PF impacting Outlook performance

I spent last weeks quite some time with Outlook performance issues in an Exchange Hybrid scenario. In addition this is not a normal Hybrid as here multiple Exchange Organizations from different AD Forests without any Trust Relationships are involved.

Thus I’m not talking about the scenario described in TechNet Multi-forest hybrid deployment scenario. It looks more like this:

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Outlook Cached Mode and TCP connections

This post was lingering around for a long time, but the last weeks showed me it’s time.

Actually I came across this topic last year just before Ignite. But somehow this topic felt into oblivion. To make it short:

It’s all about the number of TCP connections an Outlook Client establishes in a Cached Mode. Especially when it comes to shared mailbox or delegate scenarios.

What is Outlook Cached Mode?

Read more about it here. But what you really want to avoid it something like this:


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Fiddler the allrounder for troubleshooting

In my Ignite session with fellow MVP Andrew Higginbotham Troubleshooting Complex Exchange operational issues, I mentioned Fiddler as a perfect tool for troubleshooting also Exchange ActiveSync clients as well as Exchange servers itself.

After this session a lot of people reached out to me and asked me about how to do this. So I thought a write-up would be a good idea.

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