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.

sitebase

Use a custom mail server to send mails in WP. This way you can also send emails when testing on your local server. Make sure to follow us on <a href="http://twitter.com/Sitebase" title="Follow Sitebase on Twitter" rel="nofollow ugc">Twitter</a> for updates and more.

MailBase

Configure a mail server you want to use for mailing in WordPress

ElasticEmail Plugin vs MailBase