@monkeyiq Thanks for handling that! I tested the branch, but it had a little problem.
When I don't choose both "An email" and "A transfer link" just after moving to #stage3 on the transfer screen, the hide_sender_email option is displayed. I think the option should be displayed only when choosing "An email" in version 3.x.
And it would be better if the option is displayed just below the sender's email?! (Sorry, I don't know the UI policy)

I will test it more...

I'm certainly happy to test the scenario that is problematic and adjust. I sort of had the lingering feeling that there might be something that I didn't test in my use cases that is important to a particular deployment (and with a specific configuration).

I am testing on the following config.php fragment. With the hide_sender_email commented out as shown or with the commenting removed. It is also possible, though hopefully unlikely, that this interacts with some other configuration options. I would feel a bit more comfortable updating the PR to honour the advanced selector there to allow the admin to configure where this option should appear.

$config['transfer_options'] = array(
        'email_me_copies' => array(
            'available' => true,
            'advanced' => true,
            'default' => false
        ),
...
        /*
           'hide_sender_email' => array(
            'available' => true,
            'advanced' => true,
            'default' => true
        ),
*/        
...

When I don't choose both "An email" and "A transfer link" just after moving to #stage3 on the transfer screen, the hide_sender_email option is displayed.

This is a bug. You should always have something selected on the stage3 by default. I have updated things to make that the case again now.

I have also expanded this option to work on "get a link" and "email" so if somebody shares the link from an email the download page should not reveal the email address of the sender. This will not help if the user sends the link directly to a mailing list but if you share the link with $bob and then $bob sends that emailed link to a mailing list then the download page should not show $your email address.

@monkeyiq I agree the option works both "get a link" and "email".
I also tested it with this config. But the option displays outside of the advanced options area now even if advaned=true, right?

        'hide_sender_email' => array(
            'available' => true,
            'advanced' => true,
            'default' => true
        ),

Yes, at the moment advanced is ignored. Since the option is now being shown and useful on both email and transfer I think I will reenable advanced as an option again so the particular option is not special and will work as a sysadmin expects when setting advanced=true.

I think I will merge this to be part of release 3.4.