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smtp auth; who ,how, why and when?

Simon Denham

Hello,

Using exchange 2010

2x Rx connectors

  • internal network
  • gateway, anonymous permissions only.

All users use Outlook, some users work from home, most users have email on their phones. Occasionally I use OWA from the outside world.

UTM SGxxx, configured for smtp proxy, no ISP smart host

There is one website with a user enquiry form.

I have no test environment so I am loath to poke around too much. 

Questions:

Does exchange need the UTM nominated as a smart host and Why?

Does the UTM need to accept smtp auth from the internet for the outlook services described above?

  • if No? how do I turn it off (this question arises due to around 7 regular "Too many failed logins from xxx for facility smtp, blocked for 24hrs") but still allow the website enquiry form to pass.

Cheers

 



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  • 0

    Authentication it is not needed for users. The purpose of it is: A user configured in UTM can Relay directly emails (send) skipping Exchange. But that it is not allowed by most company policy.

    You can put UTM as "send connector" in Exchange (smart host) and UTM will handle the email

  • 0 in reply to Ol Deda

    The UTM is currently the smart host for exchange, super!

    The UTM is mostly configured as per Bob's setup post.

    My preference is to make the UTM do most of the work and leave exchange relatively normal.

    However, I do not understand why an external party/server would even be permitted to begin an smtp authentication, this seems wasteful and inelegant.

    • is this normal because the authentication will always fail. (and how do I have confidence this is true)
      • Is this handshake processing overhead better placed into another function of the UTM?
    • should the dubious IP address be entered somewhere to drop it at the firewall (or send it to a blackhole)?

    To prevent authentication attempts (presuming this is best practice to mitigate the smtp password guessing attacks) should "allow upstream/relay hosts only" be checked but have no listed entries, or does the check box imply a blanket function for the UTM?

    Cheers

  • 0 in reply to Simon Denham

    Please show a picture of the section of the 'Relaying' tab that includes 'Authenticated Relay' and 'Host-based Relay'.

    Cheers - Bob

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

    What is the purpose of allowing "qcds-office" to relay off the Proxy?  That's the source of your error messages.

    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 Simon Denham

    "qcds-office is the AD profile for the MFC to permit sending emails and saving to folders. In my view it only needs to send emails to internal users. this was configured by the installer of the SG115."

    Agreed with the others, Simon, that you don't want 'Authenticated Relay' and that, normally, the only thing that should be allowed to relay is your Exchange box.  Look in the Mail Manager on the 'SMTP Log' tab.  Put the IP of the HP Printer in the 'IP/Net/Address/Subj. substring:' box and you will see if emails are coming from it.  Likewise, put the sender email address of the qcds-office user in that box to see if any emails were sent from an IP other than the Exchange server.  You may not need to come in on the weekend unless the printer needs to be configured to relay off Exchange.  I'm not sure that it's that important to change the settings on the HP printer - I'd probably just leave it relaying off the UTM.

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
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