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:

OL_Con01

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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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Outlook: Issue with modified occurrences in a series

Currently I see an increasing number of reports about missing body of meeting series. As most of the series are Skype for Business and contain the dial-in information, this is really a bad end-user experience. Imagine you want to join the meeting and have no dial-in information or the attachments are gone.

My first thoughts were that this is a Skype for Business only issue or related to Exchange ActiveSync. But this time it turned out it’s not. After analyzing of several cases, it came down to an Outlook for Windows only issue in a delegate scenario.

Update 19.09.2017

The issue was resolved in Version 1706 (Build 8229.2103), which is the July version of the Current Channel. Please be aware about the changes to Office 365 ProPlus update management! You can read more about the changes here. Either way, when you are on Deferred or Semi-Annual Channel you have to wait for this fix.

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Modern Attachments behind a web proxy

With Exchange 2016 a huge improvement in regards of document collaboration with OneDrive for Business was introduced when you have a Hybrid configured.

You can read more about it here:

When I introduced Exchange 2016, I was more than happy to configure and make this feature available to my end-users. But after I run through the prerequisites and steps, I wasn’t able to get the option in OWA and with Outlook I received the following error:

ModernAttProxy01

The same happened when I was using Outlook for Mac. As different clients, protocols and servers where affected, I assumed a general issue and started troubleshooting.

Update 07.02.2018: Meanwhile a KB article was released

Modern Attachment feature doesn’t work when web proxy used in Exchange Server 2016

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Outlook for Mac in Coexistence Environment

Currently I’m upgrading an Exchange 2013 environment to Exchange 2016. In general this upgrade runs very smoothly and is almost seemless for user. It’s a complete different story when you’re coming from Exchange 2010.

So far I got only positive feedback and no issue were reported. Until a bunch of shared mailbox have been migrated.

Users complained they cannot access these mailbox anymore. First I couldn’t reproduce the issue, until I got another important detail:

All these user are using Outlook for Mac and indeed I could reproduce the behavior.

Update 04.09.2017

This issue is fixed in version 15.38 (170815) of the Insider Fast Build as of August, 16:

https://support.office.com/article/d6347358-5613-433e-a49e-a9a0e8e0462a

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How to hunt down an EAS bug

In the past month I had to troubleshoot a lot of EAS related issues. This is always a complex process and you as an administrator have to collect a lot of data and provide them to your vendors. After providing these, you often feels like a ping-pong ball. Especially when multiple vendors are involved.

Based on two examples I want to explain, how I was able to proof some misbehaviour of EAS clients. Meanwhile both have been acknowledged by the vendor as a bug:

With iOS 10 this feature can trigger a meeting forward to multiple recipients using SmartForward command.

When a user marks an item read or unread, the flag does not get synced to the mailbox.

Update 27.06.2017: There is also a fix in KB4012108 related to this issue. It’s not exactly the issue I’ve found, but a similar one. The details can be found in KB4024649.

For troubleshooting I used the following tools:

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