Extra space in subject line - plugin auto update

[22-7ths]

Keep receiving email in this manner:

ASCII based/quotedp

Subject: =?us-ascii?Q?[LONGER-SITENAME]_Some_plugins_were_automat?=  =?us-ascii?Q?ically_updated?=

Result (in Thunderbird):

[LONGER-SITENAME] Some plugins were automat ically updated

--

UTF Based/quotedp

Subject: =?UTF-8?Q?[SHORTER-SITENAME]_Some_plugins_were_auto?=  =?UTF-8?Q?matically_updated?=

Result:

[SITENAME] Some plugins were auto matically updated

So, the result in both cases (regardless of UTF, or ASCII encoding) is to add a space that shouldn't be there.

I will try disabling plugins if this isn't reproducible - but the sites only use phpmailer afaik - no smtp plugins, or the like.

[22-7ths]

Note:
This subject line DOES decode/show properly w/o the space when using an online decoder or Outlook.

Though, I'm not sure why it has a break in encoding in middle of the word 'automatically'.
Still seems like an issue?

So far, only Thunderbird and the "Webmail" we use show the extra space.

[ayeshrajans]

Are you using PHP 8.0, or Windows by any chance? There were some changes in PHPMailer with header line-end handling, that I remotely associate might be the cause.

[22-7ths]

Replying to ayeshrajans:

Are you using PHP 8.0, or Windows by any chance? There were some changes in PHPMailer with header line-end handling, that I remotely associate might be the cause.

Thanks, but nope -

phpinfo() -

PHP Version 7.4.12
System	Linux (my_hostname) 4.15.0-124-generic #127-Ubuntu SMP Fri Nov 6 10:54:43 UTC 2020 x86_64
Build Date	Oct 31 2020 17:04:09
Server API	FPM/FastCGI

[SirLouen]

Reproduction Report

Description

❌ This report can't validate that the issue can be reproduced.

Environment

• WordPress: 6.9-alpha-60093-src
• PHP: 7.4.33
• Server: nginx/1.29.0
• Database: mysqli (Server: 8.4.5 / Client: mysqlnd 7.4.33)
• Browser: Chrome 138.0.0.0
• OS: Windows 10/11
• Theme: Twenty Twenty-Five 1.2
• MU Plugins: None activated
• Plugins:
  • Micro Email Testing 1.0.0
  • Test Reports 1.2.0
  • WP Crontrol 1.19.1

Reproduction Steps

1. For testing this, I'm using a clean WP, with a Mailpit test server, basic PHPMailer configuration (provided in the bottom).
2. Using similar environment vars (PHP 7.4 with FPM/FastCGI)
3. Forced an automatic plugin update to trigger the email
4. ❌ Result of the email looks as expected (Raw email in the supplemental artifacts)

Actual Results

1. ❌ Error condition is not occurring any more.

Additional Notes

• Given that this report is a little old, and it's difficult to identify if the reporter is using a full clean server to reproduce this, I'm going to close this ticket for now as worksforme (more info below)

• If reporter is still having the same trouble and believes that can provide more detailed reproduction instructions, including, resulting raw emails, more detailed information of the WP setup (I recommend installing ​Test Report plugin) and if possible all the code that permits sending the email (or if its being sent via default mail with default server configuration), including, MTA and MTA version (for example, postfix 3.10.3) and any MTA relevant configs that could help debug this issue.

Supplemental Artifacts

PHPMailer basic config:

 add_action('phpmailer_init', function ($phpmailer) {
	$phpmailer->isSMTP();
	$phpmailer->SMTPAuth = false;
	$phpmailer->SMTPSecure = '';
	$phpmailer->SMTPAutoTLS = false;
	$phpmailer->Host = 'mailpit';
	$phpmailer->Port = '1025';
});

Resulting Email for Automatic Plugin Updating:

Return-Path: <test@example.com>
Received: from localhost (wordpress-develop-php-1.wordpress-develop_wpdevnet. [172.18.0.2])
        by 0b50bb1618fc (Mailpit) with SMTP
        for <test@example.com>; Mon, 14 Jul 2025 19:31:49 +0000 (UTC)
Date: Mon, 14 Jul 2025 19:31:49 +0000
To: test@example.com
From: test <test@example.com>
Subject: [WordPress Develop] Some plugins were automatically updated
Message-ID: <DDZDX2e8I5wCjvyvi5uMOJe5hcGc4qjNYaOcKX8iH4@localhost>
X-Mailer: PHPMailer 6.9.3 (https://github.com/PHPMailer/PHPMailer)
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8

Howdy! Some plugins have automatically updated to their latest versions on your site at http://localhost:8889. No further action is needed on your part.


These plugins are now up-to-date:
- Hello Dolly (from version 1.7.0 to 1.7.2) : https://wordpress.org/plugins/hello-dolly/


If you experience any issues or need support, the volunteers in the WordPress.org support forums may be able to help.
https://wordpress.org/support/forums/

The WordPress Team

[desrosj]

Just noting that this ​report seems similar and was marked as resolved upstream.