Extension for h5ai (https://larsjung.de/h5ai/)

Adding mailing option (Select file/s and send by email)

Workflow:

-    Select file or files (if more than one make a zip file)

-    click button for email (see attachment)

-    popup (lightbox) should open with the following fields

      o    Email

      o    Subject (with placeholder, defined in extension file)

      o    Text (with placeholder, defined in extension file)

      o    Send button

      o    Please also show the file-size

-    If the selected files exceed a certain limit (MB limitation, defined in extension file)

      o    A popup should be displayed with a warning

The extension should be in a separate file e.g. _h5ai/private/php/ext/class-mail.php

The smtp data, placeholder, limitation and warning text should be also stored there.