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  • April 1, 2026 at 11:12 am in reply to: Test-Newsletter (only) not sending after using SMPT #355475
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    Thank you, Michael. The problem is solved already! Stefano helped! 🙏🏻

    April 1, 2026 at 10:19 am in reply to: Urgent: How to disable “Precedence: bulk” header? #355466
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    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

    March 31, 2026 at 10:49 am in reply to: Test-Newsletter (only) not sending after using SMPT #355408
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    I managed to attempt a real newsletter delivery, which finally triggered a specific error message that was hidden during the editor tests:

    “SMTP Error: data not accepted. SMTP server error: DATA END command failed Detail: header Precedence is not allowed SMTP code: 550 Additional SMTP info: 5.6.0”

    It appears that my hosting environment (WordPress.com) is automatically injecting a priority header via wpcomsh_smtp_add_priority_header. My SMTP provider (Sender.net) strictly forbids the “Precedence” header, which leads to the server rejecting the email data entirely at the end of the command.

    I have already tried to remove the filter via a code snippet, but the host seems to re-inject it with a higher priority.

    Does “The Newsletter Plugin” have an internal setting or a specific hook to force-strip these headers before they are passed to the SMTP relay?

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