Urgent: How to disable “Precedence: bulk” header?

[User]

Hello Support Team,

I am using “The Newsletter Plugin” on a WordPress.com hosted site and I’ve run into a critical delivery issue after switching to Sender.net as my SMTP provider.

The Problem:
My newsletter deliveries are being rejected by the SMTP server with the following error:
“550 5.6.0 header Precedence is not allowed”

Technical Context:
It appears that my hosting environment (WordPress.com) is automatically injecting a priority header via a filter called wpcomsh_smtp_add_priority_header. However, Sender.net strictly forbids the “Precedence” header, causing the entire SMTP transaction to fail.

My Question:
Is there a specific setting within “The Newsletter Plugin” to disable or strip the Precedence: bulk header before the email is passed to the SMTP relay?

If there is no built-in setting, could you provide a specific hook or a code snippet compatible with your plugin that ensures this header is removed from the PHPMailer object during the sending process? We have already tried general WordPress phpmailer_init snippets, but they seem to be overridden by the host.

I would appreciate any guidance on how to force-strip this header specifically for outgoing newsletters.

Best regards,
Katharina

[Stefano]

Hi, try installing our “office 365” free addon that removes all the headers, probably it’s enough to solve the problem.

[User]

Hi Stefano,

I think it works again! Thank you so much! I am so incredibly relieved that my newsletter is sending again. Thank you for your advice and for pointing me toward this specific workaround.

Katharina

[Stefano]

Great! You can even open a ticket to Sender.net and ask them to just remove headers they do not accept instead of blocking emails… even if I suspect they don’t want mail marketing campaign sent with their system… but, of course, a newsletter can even be a simple communication to a small set of users…

[Stefano]

Anyway, if the header is forced by other filters, the only solution, working for Newsletter, is to install our SMTP addon. But if that filter “wpcomsh_smtp_add_priority_header” is active, your site won’t be able to send other kinds of emails.
You should contact wordpress.com.

[Author]

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