I&#x27;d recommend against PostBox.  It&#x27;s a Thunderbird derivative, so it has the same security vulnerabilities as Thunderbird does.  But it&#x27;s not updated regularly.  The current build of PostBox was last updated in November 2015. It appears to bundle Gecko (Mozilla rendering engine) 7.0.1 which was a part of Firefox&#x2F;Thunderbird 7 back in 2011. And the only version of Lightning (calendar and tasks) for PostBox is &quot;experimental and unsupported&quot; and was last updated in 2012.<p>You&#x27;re better served using Thunderbird and any extensions you&#x27;d like to tweak things a bit.