If you use CloudFlare's reverse proxy service or another similar service, you will have to make the following configuration in the "mail" record of the DNS zone to be able to send mails through SMTP.

1-. Log in to your CloudFlare account, select the website you have registered and click on "DNS".

2-. Once you are in the DNS zone in CloudFlare, click on edit the "mail" record and modify the CONTENT value you have configured to "enginelogin.com" (without the quotes).