As I was following through the tutorial on the same topic
(, I was successful in running the mail server droplet. However, the box has this warning:

Outbound mail (SMTP port 25) seems to be blocked by your network. You will not be able to send any mail. Many residential networks block port 25 to prevent hijacked machines from being able to send spam. A quick connection test to Google’s mail server on port 25 failed.

Using the command nmap -p 25 ip_address the port 25/tcp is open.
I also did command ufw allow 25. And there seems to be no issue in the virtual machine firewall side. So this is more an issue with digitalocean as discussed here on another thread:

But I have fellow colleagues that have established their mail servers in DO without this issue. My account is fairly new though and I am wondering if this has any factor in the DO’s policy. Has anyone recently experienced the same issue that I have? And is the only recourse using another mail provider such as Sendgrid? DO support is notoriously slow (been waiting for a reply on my ticket for over a week now). I need to definitely know that this is something that I need to migrate away from DO. Any help is much obliged.

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