You should never send emails from a Yahoo or AOL email address (as of April 2014) as these domains are now restricted by their DMARC policies.

It is always better - and more professional - to send emails from your own (or your business') domain name. your emails are often treated more suspiciously by recipient spam filters. If you're sending from a free email service such as Hotmail, Yahoo, etc.You must be able to directly verify when and where each contact subscribed. You must never send emails to a purchased email list or email addresses harvested from the internet. Make sure that you are sending to an 'opt-in list'.Also search for your domain name at URLVoid. You can search for your domain name at MXToolbox. Check that your domain name isn't on a domain blacklist. We automatically check all IP-based blacklists, however you may find one of your domain names has become listed on a domain-based blacklist.Note: it will take a few days for any stats to appear after you create an account with them. This will give you the ability to see various metrics that Google/Gmail keeps for your domain name and will let you see if there is a problem. Create a free account at Google Postmaster Tools.Make sure that you have added all of your domain names to the Sender Domains page, and check they are all verified.If you find that emails are being filtered into a spam folder, or junk mail folder, check the following: