I am using WP SMTP to send email and I am also using the Memberpress plugin. It looks like WP SMTP is not sending email properly, or maybe it is a WP issue. I checked with Memberpress and they told me their test emails appear to be working just fine and that I need to look into the WP SMTP/WP to find out the issue. As of right now when I try to send out test emails through Memberpress they do not go through to my email. I don't have support for WP SMTP so I am reaching out to you in hopes you have worked with situations like these before.
I keep having WP email issues and I hope this time it will be resolved for good.