503 bad sequence of commands - Fix it now ?

Email users often see the message "503 bad sequence of commands" while sending emails.
Here at Ibmi Media, as part of our Server Management Services, we regularly help webmasters and website owners to fix similar email errors.
In this context, we shall look into methods to resolve this Email error.

Main causes of "503 bad sequence of commands" ?

Some of the common reasons for this error include:
1. Faults with SMTP settings
2. Authentication issues
3. Issues with Outlook profiles

How to fix the "503 bad sequence of commands" error ?

The steps that we follow to resolve this email error depend entirely on the reason for this error.
Let us now look at the possible solutions to fix the error.

1. Enable localhost SMTP setting in IIS Application level
One of the possible solutions to fix this error in the Windows server is to enable localhost SMTP setting at IIS Application level.

2. Authentication issues
The second possible solution to fix the "503 bad sequence of commands" is to correct the authentication in your SMTP settings. We cross-check this from the SMTP properties section in the MailEnableAdmin.
We may try changing the Inbound authentication to cross-check if it fixes the error.
We will also need to ensure that "" is granted relay rights from the Access Control section.

3. Issues with Outlook profiles
Often, this error could be related to a corrupted outlook profile. Thus, a possible solution that we suggest is to try creating a new profile in Outlook and set it as default.
This helps us to differentiate if it is an issue with the outlook profile.

Once confirmed that the mails are delivering from the new profile correctly, the users are urged to cross-check the Account settings in Outlook.

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This article covers methods to fix the email error, "503 bad sequence of commands" which happens as a result of a number of reasons.

To resolve SMTP response: 503 Bad sequence of commands, consider the following and also read the complete guide here.
The IP that should be - whatever that is, look at that box, this is where the problem is likely to be.
Your internal domain is domain.com or domain.net etc.
You may also add a test email account and check if it works as expected. If this works, then this could be an issue with the email account or with the service provider.