@newbie

When it comes to e-mail, you’re going to be much better off using a transactional e-mail provider to ensure that e-mail goes through.

For example:

https://www.sparkpost.com/

https://mailgun.com

https://sendgrid.com

They all have plugins that integrate with WordPress to allow sending via their API or SMTP servers.

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The reason I’d recommend using a transactional e-mail provider is due to the fact that to successfully send e-mail, you need a valid PTR (Reverse DNS Record) as well as SPF, DKIM, and possibly even a setup for DMARC to keep mail out of the spam/junk folder on the recipients end, if they make it that far.

SendMail and Postfix will attempt to send e-mail when called by PHP’s mail() function, though even if they do send, there’s no guarantee it won’t bounce or actually make it where intended without those things configured (and that can be a bit of a hassle – both to setup and manage).

Services, like those mentioned above, work around that by providing API and/or SMTP integration on there end, which you connect to via a Plugin. You may still need to add SPF/DKIM entries to your DNS zone file as a part of their setup, but you won’t have to physically set those things up on your server as a part of a working mail server setup/configuration.

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That said, you can check mail.log in /var/log to see what is being said about the mail – whether it’s sending, failed, bounced, ect.

tail -20 /var/log/mail.log

That’s generally the first place to look when it comes to mail issues, unless another log file is used or specified.