[Mashiro]

I would also like to add additional but important information regarding all of this. Your IP address might be clean in all of these blacklists and checking services but major e-mail providers such as Google, Microsoft and other big players have their own internal blacklists! There is no public lookup for this lists and removal is not that easy. If it happens that your IP address is clean everywhere else and your mail server is setup correctly but your mails still go to spam there is a chance your server IP or domain is in the internal blacklist of the e-mail provider. I know that somewhere, for example, Microsoft has some kind of webmaster panel and such with a support section or e-mail address that can be connected to lookup the IP address and possibly request a removal of it from their blacklist. That's just an example. Google might have something similar or might not bother to deal with such things at all. Other providers could be baking their own different cake.