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https://issues.apache.org/jira/browse/CAMEL-25534?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18127240#comment-18127240
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Claus Ibsen commented on CAMEL-25534:
-------------------------------------
Backported to camel-4.22.x in https://github.com/apache/camel/pull/27838
_Claude Code on behalf of davsclaus_
> camel-mail - subject option description still says the Subject header takes
> precedence, but useHeaderSubject defaults to false
> ------------------------------------------------------------------------------------------------------------------------------
>
> Key: CAMEL-25534
> URL: https://issues.apache.org/jira/browse/CAMEL-25534
> Project: Camel
> Issue Type: Bug
> Components: camel-mail
> Affects Versions: 4.22.1
> Reporter: Federico Mariani
> Assignee: Federico Mariani
> Priority: Major
> Fix For: 4.22.2, 4.24.0
>
>
> Follow-up to CAMEL-24848, which corrected the useHeader* descriptions on main
> and camel-4.22.x. The description of the {{subject}} endpoint option was not
> touched and still states the opposite of the actual behaviour since
> CAMEL-23747 made {{useHeaderSubject}} default to false.
> h3. Reproduction
> Catalog metadata for smtp (same in imap/imaps/pop3/pop3s/smtps), on
> camel-4.22.1, camel-4.22.x and main:
> {noformat}
> "subject": { ... "description": "The Subject of the message being sent. Note:
> Setting the subject in the header takes precedence over this option." }
> "useHeaderSubject": { ... "defaultValue": false, ... }
> {noformat}
> A route that sets the header and leaves the URI without {{subject}}:
> {code}
> from("direct:a").setHeader("subject",
> constant("Alert")).to("smtp://[email protected]");
> {code}
> sends a mail with an empty subject, because
> {{MailBinding.appendHeadersFromCamelMessage}} only copies the Subject header
> when {{configuration.isUseHeaderSubject()}} is true. With {{subject=X}} on
> the URI and a Subject header, X wins, again the opposite of the note.
> In an evaluation of coding agents (Claude Code and IBM Bob) on Mule-to-Camel
> migration tasks, 25 sessions read this description through camel-jbang-mcp
> 4.22.1 ({{camel_catalog_component_doc smtp}}); at least one concluded from it
> that the Subject header overrides the URI subject, and a mail sent with an
> empty subject (Subject set only as a header) was the most frequent remaining
> defect in the generated routes (10 sessions).
> h3. Cause
> *
> {{components/camel-mail/src/main/java/org/apache/camel/component/mail/MailConfiguration.java}},
> javadoc of {{setSubject}}: "Note: Setting the subject in the header takes
> precedence over this option."
> * {{components/camel-mail/src/main/docs/mail-component.adoc}}, section on the
> message content: "The subject of the MimeMessage can be configured using a
> header property on the IN message" with a {{setHeader("subject", ...)}}
> example, followed by "The same applies for other MimeMessage headers such as
> recipients, so you can use a header property as To" and a ProducerTemplate
> example with To/From/Subject headers. With the 4.22 defaults none of these
> headers are used unless the matching useHeader* option is enabled.
> * {{MailBinding.populateMailMessage}} code comments ("the headers win UNLESS
> useHeaderSubject is set to false", same for replyTo) describe the old default.
> h3. Fix
> * Change the {{subject}} javadoc to something like: "The Subject of the
> message being sent. The Subject message header is ignored unless
> useHeaderSubject=true, in which case it overrides this option." and
> regenerate the component/catalog JSON and the endpoint DSL builders.
> * In mail-component.adoc, add {{useHeaderSubject=true}} (and
> {{useHeaderRecipients=true}}/{{useHeaderFrom=true}} for the To/From example)
> to the examples, or state next to them that the headers are only honoured
> when the useHeader* options are enabled.
> * Update the two comments in {{MailBinding.populateMailMessage}}.
> Documentation only, no runtime change. A backport to camel-4.22.x alongside
> CAMEL-24848 would keep the 4.22.2 catalog consistent.
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