Does your email bounce back with the "451 qq trouble in the home directory (#4.3.0)" email error message?
The message indicates that the SPF record check for the domain failed.
Here at Ibmi Media, as part of our Server Management Services, we regularly help our Customers to fix email delivery issues.
In this context, we shall look into how to fix email problems efficiently.
What triggers 451 qq trouble in the home directory (#4.3.0) ?
The error mainly occurs due to failure in the resolution of the SPF record of the sender domain. Before getting much deeper about the mail issue, let’s take a look at SPF record and its relevance in email delivery.
SPF record is a type of TXT record that identifies which mail servers are permitted to send an email on behalf of your domain. The purpose of an SPF record is to detect and prevent spoofing or any kind of exploit of emails.
The mail delivery was failed since the SPF check was failed. That means you have sent an email from an unauthorized server. In Plesk there is an option to decide what to do when an SPF check failed for an email transaction. When that option is set to "Reject mail when SPF resolves to 'fail' (deny)" it will bounce back with the above message.
Let's see how our our Experts fixed the issue.
How to fix 451 qq trouble in home directory (#4.3.0) email error ?
In all production servers, it is recommended to keep SPF checking mode to "Reject mail when SPF resolves to "fail" (deny)".
It will check and validate the SPF record and if it fails the email will be rejected. On account of this, it will provide protection from spam and spoofed emails.
Hence, it is not recommended to change the above settings under the recipient server. A valid solution for the email delivery issue will be examining the SPF record of the domain and correcting if it is wrong.