RFR: 2641: Mbox parser fails on headers that start with newline

[Zhao Song]

On Fri, 19 Dec 2025 15:06:00 GMT, Erik Joelsson <erikj at openjdk.org> wrote:

> It seems that at least for Mailman 3 mbox data, header values will sometimes start on the next line, after a single space, instead of directly after a single space following the `:`. E.g. this:
> 
> 
> Subject:
>  foo
> 
> 
> Instead of this:
> 
> 
> Subject: foo
> 
> 
> This patch adjusts the regexp used to parse mbox email headers to take this into account, by optionally matching this newline. Added a some more test to verify the various cases.

Looks good.

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Marked as reviewed by zsong (Reviewer).

PR Review: https://git.openjdk.org/skara/pull/1748#pullrequestreview-3599441946