Sendloop hasn't been updated since 2021. Use a tool that's actively maintained.
Sendloop's blog hasn't been updated since 2021; it hasn't tweeted since 2017; more than that, its pricing is extremely aggressive (see below.)
Email is important to your business; it's the most valuable asset you can have. Sendloop might satisfy your basic email needs, but you shouldn't trust a zombie company to deliver on your email marketing goals. If you're looking for a tool that's growing and getting better over time, Buttondown is a better choice. (Which is not even to speak of all of the other features that Buttondown has that Sendloop doesn't!)
Here's how one happy customer puts it, having switched from Sendloop to Buttondown:
Buttondown just made sending a newsletter easier all around, from formatting text to looking at analytics to see what worked and what didn't.