post-smtp

https://wordpress.org/plugins/post-smtp/

Good for failed delivery attempts, even if password changes, Sendgrid.

The Post SMTP is more feature rich and will do a scan to help you with setup and has built in log system.

Configuration with Reseller club Business Email

If using Cloudflare DNS - Make sure proxy for SMTP CNAME is not enabled on Cloudflare.

User: actual email (no alias or forwarding emails)
Encryption: none
Port: 25
Encryption: STARTTLS
Port: 587