You might want to consider TMail21 as an option. User identities cannot be spoofed (like they easily can be with email) AND every TMail from an internal address is marked with an special indicator next to it.<p>This screenshot shows the indicator (blue dot next to &quot;Ron Smith&quot;, &quot;Kevin Jones&quot; and &quot;Jill Brady&quot;) when the person is from the same company as you.<p><a href="https:&#x2F;&#x2F;tmail21.com&#x2F;wp-content&#x2F;uploads&#x2F;2014&#x2F;05&#x2F;tmail-snapshot-new.png?1" rel="nofollow">https:&#x2F;&#x2F;tmail21.com&#x2F;wp-content&#x2F;uploads&#x2F;2014&#x2F;05&#x2F;tmail-snapsho...</a><p>This would not be the main reason to use TMail21 but is a nice additional benefit.<p><a href="https:&#x2F;&#x2F;tmail21.com&#x2F;why-tmail&#x2F;mission-critical-processes&#x2F;" rel="nofollow">https:&#x2F;&#x2F;tmail21.com&#x2F;why-tmail&#x2F;mission-critical-processes&#x2F;</a>