Thank you for your interest in the plugin!
The plugin sends emails via the native wp_mail() function; I haven't tested sending the emails with Sendgrid.
However, I found this plugin (https://wordpress.org/plugins/sendgrid-email-delivery-simplified/) and its description says:
SendGrid’s WordPress plugin replaces WordPress’s default wp_mail() function by using either an SMTP or API integration with SendGrid to send outgoing email from your WordPress installation.
So I think after installing this plugin you should be able to send the emails from s2Emails via SendGrid, but as I said, I cannot guarantee it will work.
If you wish, you can purchase the plugin and test it. If it doesn't work, I will refund you the payment.
Just to let you know:
In 7 days I will upgrade my website www.s2emails.com and also the plugin. Now it will be possible to send emails also:
- after expiration
- after visiting a shortcode on a page/post
- there will be no limitation until when you can send the emails; it can be even one year after registration/expiration/visiting a shortcode
I will also increase the price of the plugin.
I have been testing the new version of the plugin on my website (www.presta-theme-maker.com), and it works great!