Match db and code default for allow_send_as
The sql table mail_forwarding has 'n' as default for 'allow_send_as'.
However in ./interface/web/mail/form/mail_alias.tform.php it's defined as 'y'.
I'd like to suggest setting the sql default also to 'y'.
The field is also missing in the API docs, "I'll add an MR for that.