IIS SMTP Virtual Server, suddenly not sending emails

Question

I have a virtual smtp server running on a machine, I have another machine that is sending emails to that and forwarding to google (smtp.gmail.com). Was working for couple years now but suddenly, stopped. It is saying error "Action: failedStatus: 5.5.0

Diagnostic-Code: smtp;530-5.7.0 Authentication Required. For more information, go to

530 5.7.0 https://support.google.com/mail/?p=WantAuthError d2e1a72fcca58-73bd23342ddsm8959795b3a.164 - gsmtp"

I know that is saying it is a TLS error, but why was it working before? Nothing has changed. Unless google suddenly tightened up their smtp server?

Answer 1

If you made no changes on this server, then it is very likely that changes on the remote server managed by Google were the cause of this problem.

This shouldn't be surprising, because the security landscape is constantly changing and evolving, and Google is very actively driving the trend.

BTW, if you were referring to "IIS SMTP Virtual Server Component" in "a virtual smtp server running on a machine", you must understand that its lifecycle ended in July 2015 and is no longer supported by Microsoft,

https://learn.microsoft.com/en-us/previous-versions/aspnet/8b83ac7t(v=vs.100)

So, you have to migrate away from such deprecated bits as soon as you can.

Answer 2

google is updating their SMTP security. along with requiring higher TSL level, they are requiring oauth authentication.

https://support.google.com/a/answer/14114704?hl=en

you will need a replacement SMTP relay.

Answer 3

Hi Lance Ricci,

Based on the error message you’re seeing:

530-5.7.0 Authentication Required

It appears that Gmail has recently updated its SMTP security requirements. I understand that your setup may have worked for years but Google now enforces stricter authentication and encryption standards, including:

• Mandatory OAuth 2.0 authentication
• TLS 1.2 or higher for secure connections

These changes are for enhancing email security.

You can read more about these updates here:
https://support.google.com/a/answer/14114704?hl=en

Additionally, it’s important to note that the IIS SMTP Virtual Server component you're using is a legacy feature that was officially deprecated by Microsoft in July 2015 and is no longer supported. This means it does not support modern authentication protocols like OAuth 2.0, which are now required by services like Gmail.

For more information you can access this document here:
https://learn.microsoft.com/en-us/windows-server/get-started/removed-deprecated-features-windows-server?tabs=ws25

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