Well not you yourself hopefully, but your email campaign actually. It happens to the best of the bunch, even to ESPs (email marketing service providers) who are supposed to know exactly how to prevent an emailing landing in the spam folder. See the GMail spam folder of one of my accounts below:

Ouch. So that’s where all the Gucci emails I was expecting went. No less than three emails within two weeks have landed in the spam folder, and nothing from Gucci in the regular inbox since 1st Nov. The main question here is: what has caused those emails to land in the spam folder in the first place? I’ve opted in for them, there is no Viagra or diploma talk in there, etcetera.
Let’s talk subject lines. The full Gucci subject line of the top message in the screenshot:
YOU ARE INVITED TO VISIT GUCCITIMELESS.COM
Subtlety doesn’t really come to mind here, and several spam filters love CAPS in subject lines -and- content of emails. Score 1 for the spam filter. Look for more info on CAPS scoring in the Spamassassin docs here.
Next up: text content vs imagery inside email. This is something compared too: when you have too much imagery compared to text, for instance one big image and just two to four lines of text, your message gets marks for that too. It can be found in the Spamassassin docs too, look for the mention of images with x amount of words. The content of the Gucci email is this:

Top and bottom two lines are regular text, the rest is one big image. Score 2 for the spam filter. But Gucci gets to score a point too: the from address (gucci@e.gucci.com) matches the mailed-by and signed-by parts of the email, so this should put them ahead a bit in the deliverability department. There are more points to be discussed, but I’d like to keep this one simple as I try to think like the spam filter.
One thing jumping to your mind of course is: couldn’t all of this be prevented by people having the from address (reply address) added to their address books, including me? It would save a lot of trouble, both for me and Gucci by whitelisting their email address. While this is certainly true and Gucci have put the suggestion to do so on top of their email (kudos for that), people are lazy and/or sometimes simply don’t want to have all those addresses of commercial senders in their address book. I have only added two out of several hundred commercial senders to my address book, for instance: or else my email address book gets so overpopulated it’s not funny anymore.
So my opinion is that address book whitelisting is not the holy grail of deliverability, but it does help in getting better inbox placement. Be keen on the quality of subject lines, email content, image <> text balance, quality of html (no broken code) and special tricky keywords (a nice basic roundup can be found here): this will hopefully help delivering those emails to the inbox instead of being shunned to spam folders.