In preparation for an open house my company is hosting, a number of test emails have been sent out to make sure that our our campaign emails are dropping in inboxes and not spam folders. 

We have had success on an organizational level but when our emails hit Gmail accounts, about half the recipients receive them in spam and the other half receive them in their inbox. 

I tried another condensed test this morning with two gmail accts that I own. One received the invite in inbox, the other in spam...

Is there a solution to this problem? 

Thank you 

Ben