How do I improve the deliverability of e-mails sent from my work Gmail?

“I'm sorry, but nothing has arrived in my inbox.”

You'll probably agree that each of us has heard this sentence at some point and spent a fair while hunting for the stray e-mail with the person on the other end of the line. After a few unsuccessful attempts you give up, send the e-mail again and hope it arrives. The question is what to do when these situations start happening suspiciously often. Where should you look for the fault? And how should you respond in that case? And how do you make sure it doesn't happen again and the problem is resolved? Let's take a look at the issue and find out how a DKIM key helps the deliverability of your e-mails.