hook_mail_alter() implementations aren't invoked early enough

I don't yet see any bug.

• DefaultsEmailAdjuster sets the sender address. If nothing sets a from, Symfony will set it to match the sender.
• LegacyEmailBuilder::build() calls hook_mail() then hook_mail_alter(). This is by design only for LegacyEmailBuilder - in other cases we don't want to call hook_mail() and we therefore can't call hook_mail_alter() because the expected values to alter won't be present.
• Email adjuster plug-ins can set a weight. If they set a weight greater than LegacyEmailBuilder then they will see the results of the above two hooks.

I kind of experience the same problem, or at least I think. It occurred during the migration to Drupal 10 while using version 1.4.0 of Drupal Symfony Mailer.

When I do not alter the From-header in the hook_mail of my custom module, the site name and mail are implemented in the From header.
As soon as I try to alter the From header in the hook_mail, it results in me getting {{ getSender(message) }} as the From name.

I added a screenshot for clarification.

@adamps, can you tell me what is fixed? Or how I can fix it myself?

Because I still experience the issue.

@AdamPS I migrated to Symfony mailer module from Swiftmailer while upgrading Drupal to 10.1 from 9 version. In my site I had a hook_mail_alter to style the register email to be an HTML mail using a Twig template. Now, the hook_mail_alter isn't called. What should I do to recover this feature? It's an strict requirement from my customer.

I finally migrated to SMTP + Mime mail and I removed Symfony mailer to preserve hook_mail_alter features.

If fixed is confusing, then let's call it "works as designed". @Wilfred Waltman and @rcodina please see #2 where I explained that everything seems to be working exactly as I would expect.

Or how I can fix it myself?

See bullet 3 in #2. You can set the weight for your EmailAdjuster to control whether you run before or after LegacyEmailBuilder.