[wp-trac] [WordPress Trac] #56779: wp_mail header ignores multiple headers with same name

[WordPress Trac]

#56779: wp_mail header ignores multiple headers with same name
-------------------------------------------------+-------------------------
 Reporter:  pentatonicfunk                       |       Owner:  (none)
     Type:  defect (bug)                         |      Status:  new
 Priority:  normal                               |   Milestone:  Awaiting
                                                 |  Review
Component:  Mail                                 |     Version:
 Severity:  major                                |  Resolution:
 Keywords:  needs-patch has-test-info good-      |     Focuses:
  first-bug                                      |
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Changes (by SirLouen):

 * keywords:   => needs-patch has-test-info good-first-bug
 * type:  enhancement => defect (bug)
 * severity:  normal => major


Comment:

 == Reproduction Report
 === Description
 ✅ This report validates whether the issue can be reproduced.

 === Environment
 - WordPress: 6.9-alpha-60093-src
 - PHP: 8.2.29
 - Server: nginx/1.29.0
 - Database: mysqli (Server: 8.4.5 / Client: mysqlnd 8.2.29)
 - 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

 === Steps
 1. Instructions as explained in OP, using two headers with same key,
 different value
 2. 🐞 Only second value will prevail

 === Actual Results
 - ✅ Error condition occurs (reproduced).

 === Additional Notes

 - I can still see your point of why someone might need to add multiple
 identical header tags (updating Mailgun
 [https://documentation.mailgun.com/docs/mailgun/user-manual/sending-
 messages/#passing-sending-options docs here])

 - In fact, this is not an enhancement, but a regression that was
 introduced in [5639]. Historically, headers added to `AddCustomHeader` in
 the `default` case. But in this commit, headers were firstly trimmed to
 their keys.

 Problem is that the fix will be a little less direct as it should because
 [https://github.com/SirLouen/wordpress-
 develop/blob/8938a326244e3fb1e27e0f64413f72fffe8467b1/src/wp-
 includes/pluggable.php#L357 some lines after] there is a
 `$phpmailer->clearCustomHeaders`

 So the solution as suggested could go, to iterate adding another array
 with id => value to the current created `default` array, and then
 [https://github.com/SirLouen/wordpress-
 develop/blob/8938a326244e3fb1e27e0f64413f72fffe8467b1/src/wp-
 includes/pluggable.php#L506 releasing those headers] with an extra
 iterator.

 Having this in mind, it doesn't look too difficult, so I will add `good-
 first-bug` in case someone wants to take this.

-- 
Ticket URL: <https://core.trac.wordpress.org/ticket/56779#comment:1>
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