There is a common way to edit footer text of a WordPress site theme, it’s by modifying footer.php file. But if you got a new update of your theme, you will lose that, the footer reverted back to the original footer file.
I’ve made a web application called Ciihuy SMTP Bulk Mail Sender for sending bulk/mass emails with a single click.
But I must say that:
We do not collect your input data on our server from this page. However if you have a bulk mail job, your data is stored temporarily on your web browser locally and deleted directly after your mailing job is done.
Some mailing servers has mailing limitation, for example you may only can send 200 emails per hour, not more. You must ask this to your service provider.
Some mailing servers lacks good mailing ability, just for example the email you send will go to spam folder of the recipient’s inbox.