Wouldn't it be nice if you could assure yourself peace-of-mind in relation to your mail delivery success rates? Now, thanks to the good people over at Litmus.com, you have a means to determine which Gmail inbox tab your promotional message will end up appearing under. OBVIOUSLY, you want your email to appear under the "Primary" tab. Landing at https://litmus.com/gmail-tabs will present you an oversized input box with their test email address for your test inbox target message.
Based on the quality of your ad copy, they're able to help you refine it until it lands under the Primary tab, every time. This is a great opportunity to sculpt spamless messages to ensure bullet-proof delivery accuracy. Just think, you have your own email ad copywriting robot. There's no reason to flail in the dark now with your promotional campaign messaging.