Why is SMTP blocked?

SMTP port 25 is blocked on all Droplets for some new accounts to prevent spam and other abuses of our platform. To send mail on these accounts, use a dedicated email deliverability platform (such as Sendgrid and Mailgun), which are better at handling deliverability factors like IP reputation.

Even on accounts where SMTP is available, we recommend against running your own mail server in favor of using a dedicated email deliverability platform.

Configure your firewall to allow outgoing traffic through ports 80 and 443.
There are a few ways to install an SSL on your Droplet, depending on where you get the certificate from.
You can point multiple domains at a Droplet and serve multiple websites from it.