Two phone screenings: first with their recruiter and second with the manager who was hiring. Then, one 4 hour technical interview session in the office.
Thorough discussion with the whole team about troubleshooting skills, various internet protocols (in particular SMTP), *nix fundamentals, AWS features, scripting skills, and configuration management software (Ansible, Puppet, Chef etc). The in-house interview was a good experience. Everyone was polite, friendly, and there was lots of laughter.
There was no whiteboard coding or anything "hands on". The questions were mostly scenario-based or "how would you..." which is great - this showed me that they knew exactly what kind of experience they needed and were not just playing games by asking trivia questions.
The manager was very transparent with me about their 'culture' as well and was candid about the type of people who would fit in, which I appreciated.
Sadly, their Seattle office shut down and I think that took the job I applied for with it. I only found out about not getting an offer through the Jobvite portal. The recruiter, still not being up front about my not getting an offer, asked vaguely a month later if I would be interested in remote-only work. She still hasn't followed up with me. This entire situation raises red flags... I can understand not getting an offer, but at least be up front about the decision or situation.
At this point, even if a remote role or one in Seattle was to open up, I would avoid SparkPost because of how bad their communication/management was. Be wary and make sure to ask questions about your team, its role in the company, and the longevity of your position.