This article will guide you on different methods to resolve #SMTP #error 451 which occurs due to the receiving server rejecting your email.
This can happen for a number of reasons but most likely is due to the recipients server being overloaded with #messages.
To fix SMTP Error: Failed to connect to server:
1. Modify the #firewall rules on the server to allow outbound connections on #ports like 465.
2. Modify the SMTP restrictions on the server.
3. Edit #PHPMailer settings like Host, Port etc.
4. Correct #DNS resolution for mail server.