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UTM 210 9.7: SMPT-Relaying: Combine authenticated and hostbased relay

Geoofa

Hello,

we use our Sophos UTM as a SMTP Relay in front of our Exchange Servers.

We have several Web applications that are hosted elsewhere an that use our Sophos as SMTP Relay - all of them figure in the list of "Allowed Hosts/Networks" under Host-based Relaying. That is working as expected.

Now I am about to configure a new Webapplication that needs to relay by user authentication. I add the user in the list of "Allowed users/groups" under "User based relay". That is working as expected.

The only problem is that by opening the "authenticated relaying", there are lots of Denied connections that potentially slow down the system, or even block user accounts after several denied connections.

I am looking for a way to limit the "Authenticated relaying" to a limited Network group (the IPs of my Web Application).

Can anybody help me?

Thanks,

George



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  • 0

    Salut, George and welcome to the UTM Community!

    It's not clear to me why you'd need to configure authenticated relaying in the UTM if it's the application doing the authentication, so I don't "see" the problem.  If Authenticated Relay in the UTM is needed, please insert a few relevant text lines from the SMTP log so that we can see the error reported there.

    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 your welcome and your reply.

    I try to explain it better:

    Most of my web applications use the SMTP Relay without identification by Account/password - The UTM allows relaying simply based on their IP Adress. So far so good.

    The new Webapplication I try to configure asks me for SMTP settings: Host/Port/Encryption/Account/Password . It does not allow to leave Account/Password empty.

    When I check 'Authenticate Relaying' and add an Account to the list it works, but at the same time I see numerous attempts to login the SMTP Server.

    So my Idea is to add a rule to allow the Authentification only for the Network of my my new Webapplication.

    Does it make sense?

    Thanks in advance for your help.

    George

    .

  • 0 in reply to Geoofa

    Merci pour les précisions, George, mais...

    Without seeing lines copied from the logs, it's difficult to analyze.

    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.

    Please find some examples below with authenticated relay enabled for a single user "allowed@123.org"

    Mails from x.y.z.a with correct authentification are treated as expected:

    2023:03:17-15:19:53 sgp-1 exim-in[23644]: 2023-03-17 15:19:53 [x.y.z.a] F=<allowed@123.org> R=<user@234.fr> Accepted: from authenticated user 'allowed'
2023:03:17-15:19:53 sgp-1 exim-in[23644]: 2023-03-17 15:19:53 1pdAvx-00069M-0r <= allowed@123.org H=123e.amazonaws.com ([127.0.0.1]) [x.y.z.a]:9024 P=esmtpsa X=TLS1.2:ECDHE-RSA-AES128-GCM-SHA256:128 CV=no A=server_login:allowed S=3004 id=07806567587dfe4b5deabsdfsdf10524d03abd@swift.generated
2023:03:17-15:19:53 sgp-1 exim-in[23644]: 2023-03-17 15:19:53 SMTP connection from 123e.amazonaws.com ([127.0.0.1]) [x.y.z.a]:9024 closed by QUIT

    But at the same time I have thousands of authentification attemps à day, like:

    2023:03:17-15:19:53 sgp-1 exim-in[23613]: 2023-03-17 15:19:53 server_login authenticator failed for (User) [81.94.195.25]:47394: 535 Incorrect authentication data (set_id=msdnaa@123.org)
2023:03:17-15:19:53 sgp-1 exim-in[23624]: 2023-03-17 15:19:53 server_login authenticator failed for (User) [81.94.195.25]:64524: 535 Incorrect authentication data (set_id=msdnaa@123.org)
2023:03:17-15:19:54 sgp-1 exim-in[23614]: 2023-03-17 15:19:54 server_login authenticator failed for (User) [230.14.93.25]:7880: 535 Incorrect authentication data (set_id=msdnaa@123.org)
2023:03:17-15:19:54 sgp-1 exim-in[23596]: 2023-03-17 15:19:54 server_login authenticator failed for (localhost) [23.48.20.14]:40002: 535 Incorrect authentication data (set_id=offers)

    What I would like to achive:

    Limit the possibility for authentication to x.y.z.a in order to get rid to the authentication attemps from other IPs.

    When I disable authentication relay completely, also x.y.z.a will not be able to transmit mail any more.

    2023:04:21-10:25:46 sgp-1 exim-in[28289]: 2023-04-21 10:25:46 SMTP connection from [x.y.z.a]:56546 (TCP/IP connection count = 1)
2023:04:21-10:25:46 sgp-1 exim-in[2198]: 2023-04-21 10:25:46 H=x.y.z.a.central-1.compute.amazonaws.com ([127.0.0.1]) [x.y.z.a]:56546 X=TLS1.2:ECDHE-RSA-AES128-GCM-SHA256:128 CV=no F=<notallowed@123.org> rejected RCPT <123@extern.df>: Authentication required for connections on TCP port 587
2023:04:21-10:25:46 sgp-1 exim-in[2198]: 2023-04-21 10:25:46 SMTP connection from x.y.z.a.central-1.compute.amazonaws.com ([127.0.0.1]) [x.y.z.a]:56546 closed by DROP in ACL

    Thanks for your help.

    George

  • 0 in reply to Geoofa

    Hello forum,

    can anybody help us understanding that issue?

    Have a good day.

    George

  • 0 in reply to Geoofa

    If you haven't resolved this, George, please insert a picture of the 'Hostbased Relay' section on the 'Relaying' tab of SMTP.

    Cheers - Bob

     
    Sophos UTM Community Moderator
    Sophos Certified Architect - UTM
    Sophos Certified Engineer - XG
    Gold Solution Partner since 2005
    MediaSoft, Inc. USA
  • +1 in reply to BAlfson

    Hello everyone,

    after some more tests here is the solution (a bit contreintuitive for me though):

    I simply add the IP Adresses of my web application to the list of "Allowed Hosts/Networks", which allows these hosts to send over my UTM SMTP relay.

    Whether my webapplication tries to authentify with username/password does not matter then. I can leave "Authenticate Relaying" unchecked.

    Thanks Bob.

    Georg

Reply
  • +1 in reply to BAlfson

    Hello everyone,

    after some more tests here is the solution (a bit contreintuitive for me though):

    I simply add the IP Adresses of my web application to the list of "Allowed Hosts/Networks", which allows these hosts to send over my UTM SMTP relay.

    Whether my webapplication tries to authentify with username/password does not matter then. I can leave "Authenticate Relaying" unchecked.

    Thanks Bob.

    Georg

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