Is it possible to use without play store?

Why use a service like this in the first place when you can simply send out mail via a VPS?

Many email services block spammers / unknown senders, especially if you start sending hundreds of mails.

Do you happen to know how that works ? I never used a service like mailgun or mailchimp. Do they use IP addresses that are not being blocked by the email services ?

So its essentially paying for the safe haven of knowing that your mail won't get blocked due to stupid policies?