Office 365 slow and unresponsive

[You might also be interested in How to Sync Active Directory to Office 365 or Google Apps]

The last couple of weeks the user experience with Outlook in online mode was terrible. Slow and unresponsive… many users complained. Downloading attachments in Outlook Web App (aka webmail aka OWA) was also very slow when compared to the same download action in GMail or even OneDrive for Business.

So I created a ticket with Microsoft support. It didn’t really help. The finger was pointed at the customer (try this, try that, config this, config that).  The problem occurred at multiple sites, multiple DNS’s, multiple ISP’s. Nothing really seemed to happen at MS side to fix this…

If you have problems with Outlook connected to Office 365, check these things (you may try to contact MS support too if you want):

1) The command ping should point to a datacenter nearby. Also the response delay should be comparable to other local sites. If not, try changing your external DNS server. The command tracert should display a ‘logical’ result. Your data packets should arrive at a Microsoft datacenter/network quite fast: your internal router ip->gateways ISP->Microsoft, something like for their network in Amsterdam; is also Microsoft. The packets should not go all over the world. If they make a giant detour your ISP is doing something wrong.

2) If you use Outlook 2013 or 2016 you can try to disable the new MAPI HTTP connection if it is enabled for your ‘tenant’ by MS.

To do this change the following key for each user (regedit / login script / reg file / gpo registry preference)


Outlook will display a message after a couple of minutes with the request to restart Outlook to make the setting effective.

3) If you use Outlook 2013 you can try to disable hardware graphics acceleration. On some computers this feature causes all kind of troubles. Replace 15.0 with 16.0 for Outlook 2016.


4) If you experience slow download speeds in webmail compared to OneDrive you can try to redirect to another MS datacenter. This can also help Outlook considerable. How to accomplish this? Office 365 decides which datacenter to use to fetch your mail by geo-locating your DNS server. It uses the record for this. In theory this means you get redirected to the nearest datacenter available. But sometimes bad stuff happens. Your datacenter is not as fast as another one… or has problems… or…

Some example Outlook service locations for Office 365:


a) Lookup a public DNS server near the physical location of the datacenter that you’re trying to use as an alternative (for example I looked up an UK DNS server to get the datacenter for western europe instead of central europe). The site lists public DNS servers for a lot of countries.

b) To check if the public DNS server functions correctly: open cmd

server x.x.x.x

Check your firewall if it does not return results. Also make sure to check the public dns server again after some time to make sure it still replies so you know it is reliable.

c) Open the Windows DNS management console

d) Right click “Conditional Forwarders” and choose “New Conditional Forwarder”

  • DNS Domain:
  • DNS Server: the DNS servers you want to redirect the request to (for UK for example and
  • Check “Store this … in Active Directory”

dd) Alternative: IF you have a DNS server that understands DNS standards you can add an A-record instead for (don’t forget the last dot!) that points to the ip addresses you want (to get the ip addresses check the result of nslookup for the destination you want). Unfortunately this is not possible with a MS DNS server because it won’t allow A records for other domains in your AD zone (“The host record cannot be created. The name is invalid.”). An extra zone is not possible too: you don’t want to make your MS DNS server responsible for all DNS settings!

e) Clear the DNS cache with the command ipconfig /flushdns

f) Check the result of ping . It should display a different datacenter than the one you first saw.

g) Go to webmail (after clearing browser cache with ctrl+shift+del) and check the difference of download speed.

In my case gives much much much better performance than … Microsoft: FIX THIS!

And when I’m at it… Outlook really isn’t a good online ‘cloud’ messaging client… to name a few big problems
Online mode:

  • Its caching of messages you recently viewed is almost non existent
  • Outlook does not respond any more to GUI events when it is downloading big attachments (it’s 2014!)
  • It’s very sensitive to network hick ups
  • Impossible to put send messages in the mailbox of the sender when using shared mailboxes

Caching mode:

  • Big OST files that get corrupted frequently or take up more and more space
  • Different search results from online mode and sometimes incomplete
  • Not suitable for roaming profiles (which in itself needs a modern replacement…)
  • The ‘improved’ 2013 ‘period cache’ is not seamless; it displays a link show more on server…
  • Indexing problems that causes incomplete search results
  • Shared mailboxes sync and usage problems (there is a policy available to make these online mailboxes but still the default is flawed)

Conclusion: MS please build a new good online Outlook client. Too much historical baggage… Update 23 February 2016: Outlook 2016 isn’t better in any way. Worrying.

Thank you.

Update 27 januari 2015: My particular issue is finally fixed by MS. Me was told it was a problem with the firmware/settings of physical load balancers. Weird thing is that it is nowhere mentioned in their ‘service health’ logs. Don’t awake sleeping dogs I guess…

Update 30 januari 2015: Well… problem ís back again with emacenter…  So still not fixed permanently.

Check your Outlook plugins too. Especially antivirus engines. Try disabling plugins to see if speed improves. Office 365 already scans your mail at server level and your local antivirus will normally scan an executable before running too.


About Stoomkracht

Scripter, programmer, Windows administrator, network/wifi engineer, thinker


  1. Dennes

    Thanks for this great article that finally made me understand the reason why Outlook/Office 365 was so horribly slow at some of my clients.
    Did the jan 27 fix alleviate all the issues you had? Because even with the DNS resolving to the emea east servers (they seem to have the lowest ping from our Amazon Frankfurt hosted Terminal Servers) Outlook 2013 still perfoms like a dog.

    • Eamacenter is slow again… To test you can use a big attachment like 24 MB. Emeawest downloads with around 5 MB/s. Eamcenter with barely 500 KB/s… I don’t understand how MS can get away with this. It also seems that MS doesn’t let you use all of your bandwidth… Google does.

  2. Igor Ybema

    Both sites now resolve to the same IP-addresses. I don’t know what they resolved to earlier. So I’m now curious what is going on. Looks like the merged both sites together (only at DNS level) and hoping for the best…
    If someone wants to do more testing, you could try to change your computers host file to resolve towards one of these following addresses. Curious about the results. (Ireland) (A’dam) (Ireland) (Ireland) (A’dam) (A’dam) (Ireland)

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