MS365 Exchange Online SMTP OATH2 Error 501 5.5.4 Invalid Domain Name

Johnnie_McCord · August 5, 2024, 10:46pm

Hello all,

I am trying to set up email notifications using MS365/Exchange Online modern Auth (OAuth SMTP).

I have followed this guide on configuring the application on the Entra/Exchange side of things: Authenticate an IMAP, POP or SMTP connection using OAuth | Microsoft Learn

I followed this guide to set up the Ignition side of things: New Features: OAuth2 Clients and OAuth SMTP Email Profiles

Within Ignition OAuth2 Clients page, both the authorization and token test are successful. The returned permissions seem to match with what is expected.

However, when I attempt to send a test email I get Error: 501 5.5.4 Invalid Domain Name

Thinking it was the Exchange domain that was incorrect, I tried multiple domains that I found online and I was either unable to connect to the Exchange server or received the same error code. (ended back on smtp.office365.com)

Looking at the logs, the error seems to be in response to the EHLO message. Some additional searching revealed that this is generally due to a poorly formatted SMTP hostname send by the client (i.e. the name of the machine requesting to send an email, the Ignition gateway here). Or the hostname not being publicly resolvable by the Exchange server.

If that is the case, my question is what hostname does Ignition provide in the EHLO message?

Has anyone experienced a similar error?

Running Ignition 8.1.37 (b2024013011)

Thanks

Eugene49 · August 6, 2024, 12:33am

my random notes, when I was in your shoe:

For email setting: follow this link, use option 1.

Hope this helps.

Johnnie_McCord · August 6, 2024, 9:53pm

Thank you for the reply Eugene but that doesn't seem to work for me. I did confirm that the SMTP Auth was enabled for the user but I am still getting that same 501 5.5.4 Invalid Domain error.

jharrell · March 13, 2026, 5:13pm

Did you ever determine the source of the hostname used for the EHLO?

If that is the case, my question is what hostname does Ignition provide in the EHLO message?

Kevin.Herron · March 13, 2026, 5:23pm

github.com/javaee/javamail

mail/src/main/java/com/sun/mail/smtp/SMTPTransport.java

ae30c2117


      
              /**
               * Get the name of the local host, for use in the EHLO and HELO commands.
               * The property mail.smtp.localhost overrides mail.smtp.localaddress,
               * which overrides what InetAddress would tell us.
               *
               * @return	the local host name
               */
              public synchronized String getLocalHost() {
          	// get our hostname and cache it for future use
          	if (localHostName == null || localHostName.length() <= 0)
          	    localHostName =
          		    session.getProperty("mail." + name + ".localhost");
          	if (localHostName == null || localHostName.length() <= 0)
          	    localHostName =
          		    session.getProperty("mail." + name + ".localaddress");
          	try {
          	    if (localHostName == null || localHostName.length() <= 0) {
          		InetAddress localHost = InetAddress.getLocalHost();
          		localHostName = localHost.getCanonicalHostName();
          		// if we can't get our name, use local address literal

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So whatever the result of InetAddress.getLocalHost().getCanonicalHostName() or InetAddress.getLocalHost().getHostAddress() is.

What issue are you having, and are you sure this is the problem?