WordPress Email default is setup to use the PHP mail() function but is unreliable. The best option is to setup the site to send email through and SMTP server. In this example I use a GSuite account, but this can be done with a standard gmail account, Microsoft account or any other email provider. We always recommend using GSuite/Gmail and Microsoft as a second option.
Postman SMTP Plugin: http://idp.bz/postman
Gmail SMTP Plugin: http://idp.bz/gsmtp
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Company Website: https://www.ideapro.com
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WordPress Codex: http://idp.bz/wordpress-codex