cubefeed

The problem: SMTP email delivery by some hosting providers can be extremely slow. This plugin reconfigures the wp_mail() function to send email using HTTPS (via Elasticemail API) instead of SMTP and creates an options page that allows you to specify various options.
Plugin Settings Options:
<ul>
<li>Enable or Disable Plugin.</li>
<li>Elasticemail API username</li>
<li>Elasticemail assigned API Key</li>
<li>Elasticemail REST API URL</li>
<li>Your account channel variable(optional)</li>
</ul>

ElasticEmail Plugin

Reconfigures the wp_mail() function to send email using HTTPS (via Elasticemail) instead of SMTP and creates an options page to manage the settings.

EverPress

Xaver

Mailster Newsletter Plugin

A Dummy Mailer for the <a href="https://mailster.co/?utm_campaign=wporg&utm_source=wordpress.org&utm_medium=readme&utm_term=Dummy+Mailer" rel="nofollow ugc">Mailster Newsletter Plugin for WordPress</a>. Requires at least version 3 of the Mailster Plugin
<blockquote>
This Plugin requires <a href="https://mailster.co/?utm_campaign=wporg&utm_source=wordpress.org&utm_medium=readme&utm_term=Dummy+Mailer" rel="nofollow ugc">Mailster Newsletter Plugin for WordPress</a>
</blockquote>
<h3>Additional Info</h3>
This Plugin requires <a href="https://mailster.co/?utm_campaign=wporg&utm_source=wordpress.org&utm_medium=readme&utm_term=Dummy+Mailer" rel="nofollow ugc">Mailster</a>.
Please note the DummyMailer may require a lot of memory so having at least 256MB of RAM enabled is recommended!

Mailster DummyMailer

A Dummy Mailer for the Mailster Newsletter Plugin for WordPress. Requires at least version 3 of the Mailster Plugin

ElasticEmail Plugin vs Mailster DummyMailer