Hi {{contact.first-name}},
I wanted to reach out to discuss a potential collaboration opportunity between our websites.
I recently wrote a detailed article on [topic] that I believe would be a great fit for [website name]. It covers [specific points], which I think could provide valuable insights to your audience.
Would you be open to featuring it as a guest post on your blog? I'm more than happy to provide additional details and discuss any questions you might have.
Looking forward to your response!
Cheers,
[your name]