[0x0000000]

DigitalOcean no longer allows SMTP, you may be grandfathered in.

[dredmorbius]

At all, or by default?

In many cases, additional services (ports) are available on request. This is largely a spam-management (outbound) issue for service providers.

[gertrunde]

Apparently you need to be a customer for 60+ days of 'stable use' before they'll enable smtp.

[rurounijones]

I setup my mailinabox instance about 2 months ago without issue.