Hi {{first_name}},
I sent a partnership proposal last week for [[your channel name]] x [[brand name]]. Since then, I published [[a new piece of content relevant to the brand's space]], which might give you a better sense of how [[brand name]] would fit into my content.
Here's the link: [[link to recent relevant content]].
Happy to discuss a format that works for your team. Let me know if there's interest.
[[Your name]]