Illuminated MAY help as that gets you on a different server that is only used by others who pay for the service.
The reason for it being marked as spam is previous, abusive, users who has given our mailservers bad reputation. Helping the mail servers reputation improve by marking the emails as not being spam may help, but will probably take a bit time before there's any noticeable difference.
That aside, content may get the emails marked as spam as well; using words/phrases that are commonly used in spam emails would for instance most likely cause that.
