First, I do not have a solution, but offer a suggestion: check your online account on web to verify that the email provider isn't marking the mail spam before thunderbird sees it.

First, I do not have a solution, but offer a suggestion: check your online account on web to verify that the email provider isn't marking the mail spam before thunderbird sees it.

Thank you for the response, but the server is not running any spam software like Spamassassin. It does run Rspamd but that is only used in checking SPF and DKIM and only rejects the connection if conditions are met. It will mark in the headers if there was a soft fail, but it has been doing that since the day I set the server up over 2 years ago (longer if we count the servers I've used before that) and Thunderbird never marked them as spam. However, just to rule out all possibilities, I bypassed Rspamd on the server, restarted Postfix and watched the next 4 messages come through marked as spam with no modifications to the headers.

Here are the headers from Mozilla notifying me of your response:

X-Mozilla-Status: 0001 X-Mozilla-Status2: 00000000 Return-Path: <0101019dda9b0e58-bb5f2a20-edb6-456f-becb-340a27d98a1d-000000@us-west-2.amazonses.com> Delivered-To: xxxxxx@xxxxxx.com Received: from mail.xxxxxx.us by xxxxxx.us with LMTP id oNHeIsFU8mm9YgwAiUMkuQ (envelope-from <0101019dda9b0e58-bb5f2a20-edb6-456f-becb-340a27d98a1d-000000@us-west-2.amazonses.com>) for <xxxxxx@xxxxxx.com>; Wed, 29 Apr 2026 18:58:09 +0000 Received-SPF: Pass (mailfrom) identity=mailfrom; client-ip=xxxxxx; helo=a27-225.smtp-out.us-west-2.amazonses.com; envelope-from=0101019dda9b0e58-bb5f2a20-edb6-456f-becb-340a27d98a1d-000000@us-west-2.amazonses.com; receiver=<UNKNOWN> DKIM-Filter: OpenDKIM Filter v2.11.0 mail.xxxxxx.us 519EC90000E8 Authentication-Results: mail.xxxxxx.us; dkim=pass (1024-bit key, unprotected) header.d=support.mozilla.org header.i=@support.mozilla.org header.a=rsa-sha256 header.s=53nfvfrgqnsfql3fo6iq4d2oyxr6lsbk header.b=UruINMsg; dkim=pass (1024-bit key, unprotected) header.d=amazonses.com header.i=@amazonses.com header.a=rsa-sha256 header.s=hsbnp7p3ensaochzwyq5wwmceodymuwv header.b=HhwcfJUc Received: from a27-225.smtp-out.us-west-2.amazonses.com (a27-225.smtp-out.us-west-2.amazonses.com [xxxxxx]) by mail.xxxxxx.us (Postfix) with ESMTPS id 519EC90000E8 for <xxxxxx@xxxxxx.com>; Wed, 29 Apr 2026 18:58:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=53nfvfrgqnsfql3fo6iq4d2oyxr6lsbk; d=support.mozilla.org; t=1777489088; h=Content-Type:MIME-Version:Subject:From:To:Reply-To:Date:Message-ID; bh=lu+ga0Ka8PAqwM7ra5zg9cW/w0f4JZY2wcPu3wLxzf0=; b=UruINMsgmTmOFvDOqbWUqbasLnHHg2X4b3xWkgSOoGP+Vklbm1Hs07B98sNCipUc r8vK45Gq+5xKThbEv9I/vP6bkeQCB1Rexh/2WMLlUUXMvhidvSHZ8/Pb/cLEeYAMGnk wJUQz/eVs379/X6A5lKCUxBT1oCEer7dRWfXuldQ= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/simple; s=hsbnp7p3ensaochzwyq5wwmceodymuwv; d=amazonses.com; t=1777489088; h=Content-Type:MIME-Version:Subject:From:To:Reply-To:Date:Message-ID:Feedback-ID; bh=lu+ga0Ka8PAqwM7ra5zg9cW/w0f4JZY2wcPu3wLxzf0=; b=HhwcfJUcarqLLunyL48r8ZpaeIrs3phmtD5AK3zm6xw7F0DXg4716cq8r6wCZxf8 EEp/K9cbWsuYWOEQuk0lD0GJtsfpF0qmA/WxU0iQJ95SoGzm+OOl6VmUx6STh9jI5cy +2m63hs8tUw08T2ZygK+hoK0ZwXU3YVMgBHctdGA= Content-Type: multipart/alternative;

boundary="===============6649098517894772276=="

MIME-Version: 1.0 Subject: david posted an answer to your question "All incoming mail now gets

marked as
SPAM in Thunderbird"

From: Mozilla Support Forum <no-reply@support.mozilla.org> To: xxxxxx@xxxxxx.com Reply-To: no-reply@mozilla.org Date: Wed, 29 Apr 2026 18:58:08 +0000 Message-ID: <0101019dda9b0e58-bb5f2a20-edb6-456f-becb-340a27d98a1d-000000@us-west-2.amazonses.com> Feedback-ID: ::1.us-west-2.55Fn+vAtbDnVeXugvv+YsUqxmqRyBI6wITuZhQVE8SU=:AmazonSES X-SES-Outgoing: 2026.04.29-xxxxxx

Let me cut to the chase.

If you have a third party antivirus product that purports ot do anything with mail especially look out foe spam and scams or it has toolbars in Thunderbird or it puts buttons in Thunderbird then there is a 99% chance that is the root cause of your problem.

Folk appear here periodically complaining of thyese spam sorting issues. Most never make any sort of reply as o if they found a solution, so I assume you the information they were given fixed their problem. So this topic has a number of see also links to the side.

The first is. https://support.mozilla.org/en-US/questions/1513371

Automatic assumption that thunderbird was broken. No reply to the initial offer of information and that is fairly typical. It is difficult to get a handle in exactly the issue when no one actually replies with what their issue really was. I suspect many just give up. They want someone to waive the log into their system and fix it solution their ISP uses and fail to accept any other approach.

I recall years ago someone identified Trend and it's toolbar, but I just suspect all antivirus as it is unnecessary for email (I use defender and it has no mail functions) and generally of questionable quality. It does not have to be good if it crashes no one knows.

This is the trend feature I am talking about https://helpcenter.trendmicro.com/en-us/article/tmka-10500

Let me cut to the chase. If you have a third party antivirus product that purports ot do anything with mail especially look out foe spam and scams or it has toolbars in Thunderbird or it puts buttons in Thunderbird then there is a 99% chance that is the root cause of your problem.

I have no third party antivirus. Hell, I don't even run Microsoft Defender. I have no extensions or add-ons in Thunderbird.

Folk appear here periodically complaining of thyese spam sorting issues. Most never make any sort of reply as o if they found a solution, so I assume you the information they were given fixed their problem. So this topic has a number of see also links to the side. The first is. https://support.mozilla.org/en-US/questions/1513371

I referenced this "solution" in my initial post: I am using IMAP to connect to the mail server but it's not running any spam detection software (like Spamassassin). I know this because it's my server and even if it was, no updates have been preformed since the first of this month and this just started happening yesterday.

Automatic assumption that thunderbird was broken. No reply to the initial offer of information and that is fairly typical. It is difficult to get a handle in exactly the issue when no one actually replies with what their issue really was. I suspect many just give up. They want someone to waive the log into their system and fix it solution their ISP uses and fail to accept any other approach.

I replied to the first person to reply to my initial post, and am now replying to yours. It's kind of hard for me to assume that the issue lies anywhere but Thunderbird. I've been doing this long enough (back when qmail was still in active development) to know that the issue can still be on my end, but the chance of that is small when I look at the facts: 1) I run my own mail sever and have been doing so since the mid 90's 2) I do not run any sort of spam filtering software on the server (such as Spamassassin) 3) My server does run Rspamd, but only to check SPF and DKIM and does not alter the headers to mark them as spam or such 4) With the exception of Thunderbird notifying me of new mail even when that new mail was spam, everything was working fine until yesterday. The only change yesterday? I restarted Thunderbird so it would stop complaining about updates 5) I have unchecked "Enable adaptive junk mail controls for this account" and ensured that "Trust junk mail headers set by" is also unchecked

I recall years ago someone identified Trend and it's toolbar, but I just suspect all antivirus as it is unnecessary for email (I use defender and it has no mail functions) and generally of questionable quality. It does not have to be good if it crashes no one knows. This is the trend feature I am talking about https://helpcenter.trendmicro.com/en-us/article/tmka-10500

As I said earlier in this reply, I do not run any anti-virus, not even Microsoft Defender.