Emails going to junk mail

I recommend to contact your web host. Most common reason of this is that some of their clients sent spam and they are blacklisted. If this is the case, they will need to contact the blacklist owners and ask for the removal from the blacklist.

If you want to be sure that the problem is not on your side you can try some tool like this -- http://www.contactology.com/check_mqs.php . It will check the text of your email and tell you if it looks like a spam. Of course, you can also try to send the same email you are sending from your domain from some gmail account to another one and you will see if it will be marked as a spam.

If everything is at the host level is ok, and the ips have not been flagged, try checking the history of the domains themselves. Maybe they've been used for spam activity in the past.

Where they new acquisitions? Do you have a new/clean domain you can try setting up just to test the email?

Hotmail tends to be strict.

Make sure you have a SPF record and DKIM enable on the cPanel account. Could also be a issue with the hosts sender domains reverse record.

Mandrill is a good (free tiered) SMTP service, just requires a few small dns tweaks and is a great tool for outbound mail from apps etc.

Does this only happen when sending e-mail to one particular provider. I know some major e-mail services are more draconian than others about blocking e-mail from certain hosting companies.

You must check that the content that you are using is spam free if the content is good than also mail going to spam than just check the ip was not get blacklist ,If ip get blacklist than also good content mail goes to junk or spam folders

Make sure you have added SPF record and enabled DKIM on cPanel.
Then check your ip address is black listed or not. If it is black listed then contact your hosting provider for whitelist your ip.
http://mxtoolbox.com/blacklists.aspx