Don't bother sending me SEO queries like "Can I make a guest post on your blog?" or "will you link to my (mostly unrelated) site?" Such emails will be ignored as spam. Sending several followups doesn't make it any less spammy; quite the opposite.
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 a topic I'm interested in and not like spam. (Sending plaintext rather than HTML also makes your mail look less like spam.)