I got also the same problem.
Tried using PHP mailer: Blesta said "Sent" but the email never arrives.
Tried using SMTP (own server/cPanel and Sendgrid): Blesta said "The email failed to send due to a configuration issue", email also never arrives.
The simplest solution that works for me: I had to change my email address (sender) from admin@domain.com to admin@sub.domain.com
sending emails from root domain never works despite which SMTP server I use (also tried all configs: SSL, TLS, and Non-SSL).
Don't know what the cause.
