In order to help you with this you will need to provide more information:

• Is this a self built application or something pre-built? If it's something pre-built, let us know what software you are using.

• What mail server (MTA) have you installed on your droplet and what steps did you take to configure it.

• What errors if any are you seeing in your mail logs on this droplet?

• Are you attempting to send mail to a domain that is configured on this droplet?

my configuration.yml file has the following content

 production:
   email_delivery:
     delivery_method: :async_smtp
     smtp_settings:
       tls: true
       enable_starttls_auto: true
       address: "smtp.gmail.com"
       port: 587
       domain: "mydomain.com"
       authentication: :plain
       user_name: "mymail@mydomain.com"
       password: "mypassword"

I am trying to send test mail to see if email notifications are active

In my droplet install postfix following the Help guide