Could you please add a "Reply-To" to the email header?
This is because "Reply-To" is used by many SMTP servers to detect spam. We know that it reduces the chances of E-mails created by this plugin passing through SMTP-servers successfully. The basic usage of E-mail is that you can reply to the "From" in the header as it is, so we would like to follow that basic setting as an initial setting.
Of course, users are free to arbitrarily modify the mail-header part of this plugin.
As a side note, if there are other plugins that have the ability to modify the mail-header part on the Admin-Window, we recommend that you install them. The reason is that when the user "want to delete the added header part", we think it would be better to be able to easily delete it on the Admin-Window.
( 2023/March/07, 14:01:35, JST )