Once you've selected who you're reaching out to, Streak gives you options to customize how your message appears for each contact.
You can personalize your mail merge with variables from your pipeline columns. The more data you have in your pipelines or .CSV file, the more options you'll have for customization.
Variables can include the person name or any other data you have about them in your Streak Boxes.
You can access variables from the bottom toolbar in the Compose window: