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Description

I am trying to use "Default MAIL-SERVER" (port 2525) receive connector as an authenticated external relay. I am successful with the mailbox "Bob.smith@domain.com" but I am unable do it with "administrator@domain.com".

Permissions

Command

Get-ReceiveConnector -Identity "Default MAIL-SERVER" | Get-ADPermission -User administrator | ft AccessRights, ExtendedRights, Deny

Output

AccessRights        ExtendedRights          Deny
------------        --------------          ----
{ExtendedRight}     {ms-Exch-SMTP-Submit}   False
{ExtendedRight}     {Send-As}               True
{ExtendedRight}     {Receive-As}            True
{GenericAll}                                False

Event Viewer

The following error was logged in the event viewer;

The account 'Domain\administrator' provided valid credentials, but is not authorized to use the server; failing authentication

Event Properties

  • Event ID: 1020
  • Source MSExchangeTransport
  • Task Category: SmtpReceive

Error on client

I receive this error when trying to send a mail using System.Net.Mail SmtpClient

The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.1 Client was not authenticated

Update

I turned on "Verbose" ProtocolLogging for the receive connector and identified this entry in SmtpReceive

Inbound authentication failed as we reject well-known account authentication for Domain\administrator

How do I allow well-known account authentication without SSL/TLS?

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Why are you using administrator? Setup a dedicated account for this task, which does not have high level permissions which you are passing over the internet, and relay with that. I wouldn't dream of using administrator for anything external.

  • we were initially testing the relay and came across this issue. Of course, it is against our policy to save administrator password in an application to send emails. However, I see from documentation that it should be possible to do it if the admin has ms-exch-smtp-submit permission. My question is, why doesn't it work? – Lordbalmon Feb 24 '17 at 12:45

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