Outlook 2011 & BPOS flooding the network


  • Hi,


    We have found several instances of Outlook 2011 connecting to the Microsoft Online BPOS mail servers while using up most of the local bandwidth. For example, one particular mac sent over 20 gigs to the server in less than 24 hours. This utilization is constant once it starts, and it was not due to large volume e-mails being sent. This happes frequently on some of the Macs in my company. We are running Snow Leopard with all updates applied to the OS as well as ms Office, and running through the single sign on client.


    We have had some success inwiping out the local account, and then reconfiguring Outlook through the client.  It is at the point where some users can't even send e-mail due to the saturation. This ONLY affects Mac computers, but not all are affected. The Windows users are never experiencing this issue. Any thoughts?

    Sunday, September 4, 2011 11:52 AM

All replies

  • Greetings Rdb_statenisland!

    I have to admit that I've not heard of this sort of thing.  If it were a Windows based machine, I would suggest you look at what other applications are running at the time.  Another thing you can do is to run our speed test to see if it's truly the connection.  The speed test can be found at  The regional sites are and 

    I hope that helps!

    Vickie - BPOS Technical Support
    Got an Office 365 question? Try the Office 365 Community Forums
    Thursday, September 8, 2011 4:47 PM
  • Hi,

    Wow. Great to hear somebody else experiencing the same problem. We have a customer that is experiencing the exact same issue. Our customer is at their wits end and is about to march us out of the door because we can't resolve it and they believe that it's our hosted exchange platform or the ADSL broadband we provide that is at fault.

    I can tell you, this is almost certainly nothing to do with BPOS because the customer that has this problem has a private, hosted SBS 2008 server. My bet is that it is Outlook 2011 however we cannot reproduce the problem in a test enviornment but we now understand what is happening from hour monitoring the customers network.

    Basically, what happens is that something in Outlook 2011 triggers it to sync back all of the messages in the local to the server. We cannot identify what triggers it, but when it does and the user has a large mailbox, something gets out of sync and Outlook uploads data back to the server and chokes their upstream bandwidth.

    We have been trawling the Internet for months for information hence the reason I stumbled on your post. I once found a post of an identical problem on the forum at but within a week of posting and receiving lame suggestions from MVPs (eg. do not keep more than few hundred messages in inbox folders and archive off your mail) the forum was pulled down and replaced with a new one with none of the original content.

    How large are your user's mailboxes? The ones we are seeing problems with are 10+Gb with 10,000s of filed messages in deep folder hierarchy. My thought is that Outlook 2011 cannot handle big mailboxes with deeply nested folder trees, but that is just a hunch and based on the fact that we cannot reproduce it in a lab with test mailboxes of 1-2gb.

    Would be interested to know if you have found out any more since you posted.





    Thursday, September 15, 2011 2:14 PM
  • Hi,

    You're both not alone.  Our company recently bought several copies of outlook 2011 for mac because we primarily run off apple computers.  Thought it'd make everything faster since we were previously logging into remote desktop to check emails but it's made it worse!

    Rdb's solution of removing the account and throwing it back on is exactly what we've been doing to minimize the issue but that isn't an actual solution.  Hopefully someone will have a good answer for this.

    Thursday, September 15, 2011 5:35 PM
  • ITRyan. Thanks for your input. May I ask what version of Exchange you are running?
    Friday, September 16, 2011 4:04 PM
  • Hi all..


    I have no new updates on this except that it is still happening now and then. We are using BPOS, so whatever exchange server Microsoft Online is running would be the verson.

    We see this issue on large and small mailboxes, and so far no one seems to be able to explain it. I've been playing with the native mail app in Lion, and have been able to get that to work with iCal and Addressbook to see if we can wean off Outlook for mac, or even if Outlook is the cause. Glad to hear I am not the only person seeing this problem!

    Friday, September 23, 2011 1:03 AM
  • Same problem here, high BW long connections to:

    I have wireshark traces, but it's all ssl traffic, so not much help without knowing something about the application.

    Office 2011 on OSX lion. Account is 3 mos old, less than 500 messages in inbox.

    Completely recreatable. - start outlook.

    Sunday, September 25, 2011 5:02 PM
  • Just for completeness, this is Outlook for Mac

    version: 14.1.3 (110805)

    The more I look into this the worse it gets. Looking back at my FW logs, 70% of ALL BANDWIDTH has been used by this one outlook installation.

    I work remotely from home and this one app is killing by internet connection.

    Please let me know what additional information you need, this is not acceptable. If someone from msft can give me a private upload link I'll post wireshark captures from this.

    Sunday, September 25, 2011 5:19 PM
  • Thanks for the tip on recreating the identity. We did this last week for a user that was hammering and saturating upstream (1mb) bandwidth and it cleared the problem. OK, it redownloaded their mailbox from the Exchange server but over 20Mb ADSL2+ that didn't take too long.

    What we have since noticed is that there are discrepancies on the user's server copy and their local cache. e.g. Tasks items between local and server were completely different..also, a bunch of messages suddenly appeared in Junk E-mail from early August when user sync'd new local copy.

    Its as if local cache and online mailbox get out of sync and Outlook 2011 is contantly trying to catch up but never quite does.

    Outlook 2011 seems nasty to me..user also complains of it being slow and unresponsive aswell but is a complete Mac Fan-boy and will not give it up.

    I doubt that we are going to get much help here on the BPOS forum, but keep sharing your experiences guys and hopefully we can build a picture and get the right people from MS looking at it.

    • Edited by Nippertje Tuesday, September 27, 2011 11:43 AM
    Tuesday, September 27, 2011 11:41 AM
  • I have the exact same problem with Outlook 2011 for MAC.  Just clobbers the internet connection and there doesnt seem to be a simple fix.  Another way I found to fix it is to ensure that no messages are having a hard time syncronizing.  What you can do is empty the cache for your email folders and see if that helps.  To empty the cache, hold down CONTROL and click the folder In the folder list, click Folder Properties, and then empty the cache. If the folder contains thousands of messages, It may take several minutes to synchronize with the server.

    In the meantime is Microsoft looking into this one, its a pretty brutal problem and can kill an offices bandwidth.

    Thursday, October 13, 2011 9:49 PM
  • We are seeing the same problem with our hosted Exchange offering and Outlook 2011.  Uses all of the available bandwidth.


    Any ideas?

    Thursday, November 10, 2011 10:33 PM
  • It's been 2.5 months since I started this thread and issue still randomly comes back for some computers. For the record, the affected computers are all running Snow Leopard, we don't have a lot of machines running Lion yet.

    I have the native Mail app configured for BPOS on my Lion machine, and it seems like it is at lightspeed compared to Outlook 2011. I don't know if that's something worth trying on your end, but thought I should mention it.

    I've seen Outlook 2011 take over 48 hours to download a users mailbox, while on Windows it is done in less than an hour. Mail for mac completed in less than an hour as well. I hate to say it, but we've started to accept the reconfiguration workaround as almost normal S.O.P. now, as there's been no help anywhere with this.

    Wednesday, November 16, 2011 3:40 PM
  • Just found this thread and I'm hoping to hear about a fix soon...

    After excessive reports of extreme slowness at our remote site, I found that we see a lot of traffic between the only Mac there and our exchange environment using a netflow analyzer.  The users MB is about 2.5GB.  We've tried setting outlook to download headers only, but this doesn't seem to have helped.

    • Edited by JBrentG Monday, December 5, 2011 8:02 PM
    Monday, December 5, 2011 7:38 PM
  • I have seen this many times before, and actually helped fix this for a customer.  I would recommend checking the error logs for Outlook 2011.  Multiple possible causes:

    1.  Sending mail over 30 MB, if Outlook 2011 is not fully patched, can cause a storm of retries
        - However, this issue SHOULD be fixed, so, if you have indication that there is regression, please let us know ASAP so we can get this resolved.
        - This is an issue with EWS not sending back the proper message to Outlook 2011/Entourage 2008 WSE when sending an oversized mail
        - This sounds like the issue, and I would be very disturbed to see a regression in this in the latest SP that is applied to Exchange 20007
          - The only reason I would be hesitant to agree that this is the cause is that I monitor a customer with several thousand Outlook for Mac 2011 and they haven't indicated any regression.

    2.  Check the size of the packets, OSX LOVES to be "helpful" and send as large a message as the network will handle.  A possible cause, but doesn't usually send more information than the mailbox contains as has been indicated in this thread.

    Can you confirm if this is resolved permanently with the reconfigure, or is it a temporary fix?
    Can you somehow identify if it is the same email being sent over and over?
    Can you confirm if this affects all your users, just a few, or is it completely random?
    Can you confirm if this triggers by sending an email over 10MB or over 30MB?

    If it wasn't difficult, it wouldn't be fun, but why's it got to be this much fun.
    Tuesday, December 13, 2011 6:56 AM
  • Hi all,

    Just to let you know that I bump into the same issue (Exchange 2007 SP3 rollup 7, Outlook 2011 SP2), but I got a pending ticket with Microsoft support.

    I've been able to look at the HTTP traffic (disabled SSL on the /EWS application in IIS), and a 16Mb POST request is constantly sent to the server : 

    POST /ews/exchange.asmx HTTP/1.1
    Host: <HIDDEN>
    From: <HIDDEN>
    User-Agent: MacOutlook/ (Intel.Mac.OS.X.10.6.8)
    Accept: */*
    Accept-Language: fr, en;q=0.5
    Content-Type: text/xml; charset=utf-8
    SOAPAction: ""
    Content-Length: 16196800
    Accept-Encoding: gzip
    Connection: Keep-Alive

    The support team will get back to me on Wednesday. Will keep you updated.

    Christian G.

    Monday, April 30, 2012 4:53 PM
  • Hi everyone,

    I am not an IT professional just a university professor that had this same problem while working from home and on campus. As many have reported already I noticed that outlock 2011 (version 14.2.1) had problem synchronizing between my iPhone, MBP and iMac. So after several different paths before and after I read this post, I noticed that an email that I read in one device appeared as new in another one. In addition when I looked at the folders trying to synchronize the number of deleted emails/items in my MBP were different from the ones in my iMac. So, I manually deleted everything in the folder named Deleted Items in Outlook in both computers and I am happy to report that my download speed is back to normal and outlook is no longer maxim out my upload speed. Outlook is working great again. Hope this help and my apologies for the lack or misuse of technical jargon. 

    Tuesday, May 8, 2012 5:16 PM
  • I have almost the exact same situation here.  My problem is with an Exchange 2010 SP2 server moved to a colocation facility.  We are having bandwidth chewed up by Entourage EWS and one Outlook 2011 user (as found via our netflow analyzer).  A total of eight Mac users are causing at least 50% of our bandwidth usage and spiking our fees with our hosting facility.

    I'm sure it has to do with a constant attempt to resync the mailboxes, but I have no answer as to how to stop that.  Currently I have them downloading just headers, or checking via OWS, but neither is a viable long term solution for various reasons.  Any suggestions or solutions from anyone?  I would hate to have to clear the cached version of all 8 mailboxes and re-download them, but am willing to do that as a last resort.

    Wednesday, May 9, 2012 5:06 PM
  • Problem solved for me, have a look here :;EN-US;935848

    Indeed, when looking at the HTTP requests going on, the response of the server was '507 Insufficient storage'.

    Christian G.

    Monday, May 14, 2012 11:20 AM
  • No official comment or fix yet???  We are seeing this problem and it brings our poor T1 to a crawl.  Current OSX 10.7.  Current Office/Outlook for Mac patches.  Hosted Exchange on Office365.  "Sometimes" a particular Mac on the network will consume 100% of our outbound bandwidth -- indefinitely.  For us it seems to revolve around a large message in the Deleted items folder not cooperating the O365 Exchange server.

    Our fix (if we can call it that) is tracking down the particular Mac and then emptying the Deleted items folder and then restarting Outlook.  The problem immediately goes away -- for a while at least.  Not really an acceptable scenario IMHO.  This discovery process is quite involve for an organization that is going with the Hosted Exchange solution *because* they don't have a local computer guru.

    This problem inevitably resurfaces when someone deletes a large message.

    Ugly... very ugly.

    • Proposed as answer by 10-100 Friday, October 12, 2012 12:09 PM
    • Unproposed as answer by 10-100 Friday, October 12, 2012 12:09 PM
    Tuesday, May 22, 2012 6:53 PM
  • Hi all,

    I have a netowrk with 100 office for mac installed, only 5 have this problem.

    I completely removed office and all identities

    i performed a safe boot, for deleting caches

    i copied office folder form a workstation without the problem, i reconfigured the client and now problem seem fixed.

    hope this helps


    Monday, October 29, 2012 11:14 AM
  • Hi Federico,

    Did these steps you mentioned work long term too? Would be good to know if it's just not a temporary fix.

    Tuesday, November 12, 2013 12:41 PM
  • Hi, unfortunately not.

    i got some wks that, after DB rebuilt, now generate 400MB every 15mins.

    really hope that MS fix this ASAP.

    Monday, January 20, 2014 4:40 PM