[RichieBoy67]

Start here and check

http://mxtoolbox.com/blacklists.aspx

Make sure your dns and your email server are set up according to anti spam regulations. Once you are sure you are ok contact Google to have them re include you. i have been through this before and it can be a pita.

Make sure your emails comply or they will eventually block you totally. Not only does your dns need to be set correctly with reverse mapping, etc but you need opt in link, opt out and make it easy for people to unsubscribe because a few people marking you as spam is also all it takes even if your settings or correct. I would also check Microsoft mail and yahoo because they probably have done something as well.