Some tips: I get a lot of spam and so I have fairly aggressive spam filters; but I don't want to miss mail from real people. Please be very specific in the subject of the message, so it looks like an interesting topic and not like spam. Sending plaintext rather than HTML also makes your mail look less like spam.
Some ISPs block our server (apparently because it's served off SBC DSL and they can't distinguish fixed IP addresses from dynamic ones). Roadrunner cable and AOL block us; Earthlink may filter us into a "suspect email" folder.