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Outlook won't send email Office 365 hosted Exchange

MikeJeffers

Hi folks. I just migrated off a Juniper SSG 5 to UTM so I'm new to the product. I'm having a weird problem with my Outlook 2016 client and my Hosted Exchange instance.

 

Everything in Outlook seems to function properly, but it hangs up when trying to send email.

 

I resolve autodiscover.mydomain.com in DNS fine and Wireshark shows lots of activity with Exchange, but its encrypted.

 

 I found a number of posts discussing routing inbound mail through UTM before delivering to the client, but I'm not interested in doing that. This problem is purely the Outlook client behind UTM 9 connecting to Exchange.

 

I created a firewall rule allowing all ports from the host running Outlook to any IP, but it still doesn't work.

 

Any thoughts?



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  • 0

    Does #1 in Rulz give you any hints?

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • 0 in reply to BAlfson

    Hi Bob. Thanks for the lead. Rulz is really helpful. That said, I don't believe IPS is a problem with Outlook sending email. I've checked and IPS is globally disbaled and I've reviewed the sub-settings under IPS and they're all disabled as well.

     

    FWIW here's a tad bit more about my Outlook connection:

    My mail is hosted at Exchange Online as part of my Office365 subscription. I'm using Outlook Anywhere and from what I'm reading it is RPC over HTTP. I know Microsoft is moving to MAPI over HTTP, but I can't say for sure if my deployment has been changed to that. (I'm opening a case with MS to verify).

     

    I'm not behind the UTM at the moment, so I've run a Wireshark capture and all I can see is TCP 443 to Microsoft while sending mail. I'm going to conduct this same experiment later when I am behind it.

  • 0 in reply to MikeJeffers

    Traffic on 443 may be caught by the webfilter if you use webfiltering. You can try to disable webfiltering temporarily and see if Outlook is then able to send mail. If so, you may need to add exceptions to the webfilter.

    Strange thing however is that at our company we also use Office365 mai and we have no problems with it behind a UTM (with webfiltering enabled).

    Managing several Sophos UTMs and Sophos XGs both at work and at some home locations, dedicated to continuously improve IT-security and feeling well helping others with their IT-security challenges.

    Sometimes I post some useful tips on my blog, see blog.pijnappels.eu/category/sophos/ for Sophos related posts.

  • 0

    The problem turned out to be a known MTU bug on the external interface. I'm a cable modem subscriber and UTM was setting the external interface MTU at 576. I disabled the MTU auto-discover feature, manually set the MTU at 1500, and several of my UTM problems disappeared.

    https://community.sophos.com/products/unified-threat-management/f/hardware-installation-up2date-licensing/80641/sophos-utm-9-407-3-released

     

    I'm not sure how this is related to sending email in Outlook, but it was.

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