We tried using FastMail for our (small) company, but switched after ~8 months because we started running into deliverability issues and countless issues with shared calendars being unshared (or sometimes losing events).<p>We also couldn&#x27;t use any of the nice sales tools that integrate with Google Apps (or any of the tools that make managing calendars easier, like <a href="https:&#x2F;&#x2F;claralabs.com&#x2F;" rel="nofollow">https:&#x2F;&#x2F;claralabs.com&#x2F;</a> or <a href="http:&#x2F;&#x2F;boomerangcalendar.com&#x2F;" rel="nofollow">http:&#x2F;&#x2F;boomerangcalendar.com&#x2F;</a>). We&#x27;re now on Google Apps and very happy.