How can I ensure that emails generated by the server/Wordpress don't end up in spam?

I’m not trying to run my own mail server, so email for this domain is hosted elsewhere. But, of course, Wordpress needs to send email (woocommerce orders, password reset notifications, contact forms etc) from the domain. Human to human email is fine, but any emails from the website itself go directly to spam. I have mx records and an spf record that I got from the email host. I have edited the spf record with the addition of include:mydomainexample.com, (in addition to the original include:exampleemailhost.com) but I’m not sure that’s the correct domain with my setup?

It seems like maybe I need to install Postfix to properly send email from my own server. I’m prepared to follow this tutorial: https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-postfix-on-ubuntu-16-04

However, it seems like this tutorial is aimed at users who have one domain per droplet? I use the LAMP stack and have multiple virtual hosts. Is there different steps involved if I wanted to properly configure sending email from each domain I have associated with my droplet?