To get port 25 opened for your account, you need to create a Support Ticket from your account.

A small number of new accounts have SMTP blocks placed on them by an automated system based on a number of factors. If your account has an SMTP block you would not be able to connect to any service running on port 25 on a remote server. This can be tested using telnet.

If you are running a local firewall on Ubuntu you can temporarily disable it with the command service ufw stop to see if you can then connect.

Note that we do block SMTP on ALL ipv6 addresses. If you are using ipv6 on your droplet you may need to configure your mail agent to ensure that all SMTP traffic is sent over ipv4.