How to Set Up Postfix SMTP Relay on Ubuntu with Sendinblue
This tutorial is going to show you how to set up Postfix SMTP relay with Sendinblue on Ubuntu. Postfix is a popular open-source SMTP server. Previously I wrote an article on how to easily set up a full-blown email server on Ubuntu with iRedMail, which helped a lot of readers run their own email servers.
However, some readers told me that port 25 is blocked by hosting provider/ISP as a way to control email spam, so they couldn’t send emails. Vultr would unblock port 25 if you ask them to, and ScalaHosting doesn’t block port 25 at all, so I recommend using ScalaHosting VPS. Some other hosting providers/ISPs like DigitalOcean would refuse to unblock port 25.
You can bypass port 25 and send emails via SMTP relay because it uses TCP port 587. With SMTP relay, your own email server doesn’t directly send email to the destination email address. Instead, there’s an intermediate mail server, also known as smart host or relay host, that sends emails on your behalf. Your email server communicates with the relay host on TCP port 587, then the relay host communicates with the recipient’s mail server on port 25.
SMTP relay can also help you get around anti-spam blacklists, if your IP address is blacklisted for whatever reason. The recipient’s mail server checks the relay host’s IP address against public anti-spam blacklists, instead of your server IP address and because SMTP relay services maintain good IP reputation, so your emails can get through IP blacklists.
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