WordPress has a function called wp_mail for handling mail delivery job. This function requires PHP’s send_mail function to work. Unfortunately, not all web hosting providers enable PHP’s send_mail function. As a result, your WordPress site won’t be able to deliver an email. To fix this issue, you can install an SMTP plugin.
A common error usually occurs when the hosting provider you use disable the PHP’s send_mail function is the form you created with Contact Form 7 doesn’t work since Contact Form 7 and most form builder plugins use WordPress’ wp_mail function for mail delivery. The problem is getting more complex is you use WooCommerce since most transactions involve emails.
How an SMTP Plugin Works
Some WordPress sites prefer to use an external SMTP server even if their hosting provider enable the PHP’s send_mail function. The reason is that emails sent using WordPress’ wp_mail function often send up in users’ spam folders. An SMTP plugin plays a role to replace the WordPress’ wp_mail function job. Some SMTP plugins allow you to use your own SMTP server (if you have one) or use third-party SMTP services such as Gmail, Mailgun, and Amazon SES.
6 of the Best SMTP Plugins for WordPress
1. Post SMTP

Post SMTP is a great solution if you have just created a form with Contact Form 7, Elementor or your favorite form builder but the form doesn’t work due to the mail delivery issue. Post SMTP allows you to turn your Gmail account into an SMTP server. We have written the tutorial in this post if you want to learn more. In addition to Gmail, Post SMPT also supports Mandrill, SendGrid, and Mailgun. Post SMTP is pretty easy to configure and it’s free to use.
2. Easy WP SMTP

Easy WP SMTP is a better-suited option if you already have an SMTP server and want to use it to your WordPress site. You just need to enter the SMTP Host, post, encryption, and login info. Basically, most hosting providers already have an SMTP server. You can request your hosting provider for the SMTP details of your site. Easy WP SMTP is also free to use.
3. Gmail SMTP
As the name suggests, this plugin is designed specifically for Gmail. So, if you want to use Gmail as the SMTP server on your website, you can use this plugin. On the configuration process, you need to enter the client ID as well as client secret which you can get via Google API Console. It takes more effort, but better in terms of security. Gmail SMTP can also be used for free.
4. WP Mail SMTP

WP Mail SMTP is an SMTP plugin developed by WPForms. So, if you use WPForms as your form builder plugin, it can be a great complement although you can also use it for any form builder plugin. WP Mail SMTP is one of the most feature-rich SMTP plugins as it supports nearly all SMTP servers. From Gmail, Amazon SES, Outlook, SendGrid, Sendinblue, Mailgun, and so on. If you have your own SMTP server, you can also use it on your WordPress site with this plugin. In addition, WP Mail SMTP also comes with extra features including mail logs and notifications manager. WP Mail SMTP is a freemium plugin.
5. SMTP Mailer

SMTP Mailer is a free SMTP plugin developed by the same developer as Gmail SMTP. The difference is this plugin doesn’t build specifically for Gmail. You can use SMTP Mailer for any SMTP server by entering the SMTP host, SMTP login, and SMTP port. A standard feature like mail testing is available.
6. WP Mail Bank

WP Mail Bank is a feature-rich SMTP plugin for WordPress. In addition to allowing you to set up an SMTP server for your WordPress site, it also comes with a report and notification feature. WP Mail Bank can be used to configure Gmail to be an SMTP server. It comes with a setup wizard feature to make the configuration process gets easier. In addition to Gmail, WP Mail Bank also supports Office 365, Yahoo, SendGrid, and Mailgun. However, you need to use the pro version to configure SendGrid and Mailgun. Yes, WP Mail Bank is a freemium plugin. Another pro feature offered by WP Mail Bank is a role manager. This feature allows you to control who can use WP Mail Bank on your WordPress site.