How to Choose the Right Mass Mail Service Provider?

I'm looking for a reliable mass mail service provider for sending newsletters and customer updates. While researching, I came across DigitalAka™ Mass Mail Service Provider solutions and wanted to know if anyone has experience with them or similar platforms.

What features should I prioritize, such as deliverability, SMTP support, automation, analytics, or scalability? I'd appreciate recommendations and real-world experiences before choosing a mass mail service provider.