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503 bad sequence of commands – How to fix

by | Apr 23, 2021

Email users often see the message “503 bad sequence of commands” while sending emails.

As a part of our Server Management Services, we help regularly webmasters and website owners to fix similar email errors.

Let us today discuss the possible reasons and fixes for this error.

Common reasons for “503 bad sequence of commands”

Our Support Engineers have seen quite a few cases where email users receive this error while sending emails.

Some of the common reasons for this error include:

  • Faults with SMTP settings
  • Authentication issues
  • Issues with Outlook profiles


How to fix the “503 bad sequence of commands” error

The steps that our Support Engineers 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.

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.

Authentication issues

The second possible solution to fix the “503 bad sequence of commands” is to correct the authentication in your SMTP settings. Our Engineers 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.

Issues with Outlook profiles

Often, this error could be related to a corrupted outlook profile. Thus, a possible solution that our Engineers 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 Outllook.

[Need any further assistance in fixing Email errors? – We’re available 24*7]


In short, the “503 bad sequence of commands” error triggers due to a number of reasons. Today, we saw some of them and how our Support Engineers fix them.



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