[Mashiro]

If you using a custom DNS service such as Cloudflare the part of the guide is not really applicable to you. You can continue from "How to Install and Setup Mail Server on Ubuntu 18.04" I would say in that case. That said you will have to setup some DNS records at Cloudflare later on like MX records, SPF and such. The following might be a shock for you and others but I never bothered to setup a mail server on my own server at my own because it is too much hassle these days with all the necessary work to get the mails to work and not be blocked or land in spam. So I'm not really the correct person to ask in that case. Sorry about that .

If you plan to use your own mail server on the VPS you still need a plugin that will allow you to configure the wp_mail() function to use the server. I found this guide: https://coderwall.com/p/hogffa/sending-e...-localhost

It's basically the same plugin that I linked before . Instead of hosting your own server you can also use the free Sendgrid plan which allows 40.000 mails for the first 30 days and then 100 mails per day. If you don't exceed 100 mails / day this should work better initially than the hassle to setup a properly working mail server.

So you can use the plugin together with Sendgrid to send out mails. I used to do this on the Wordpress blogs I hosted and we still do it at FreeVPS.us (well, the Sendgrid account is enabled and configured for it, but because it is closed no e-mails are being sent obviously unless someone does something like "Forget password" or similar).

Other 3rd party SMTP services with free plans are:
- MailGun (10.000 mails / month)
- SendInBlue (9.000 mails / month)