Emailing service

I am going to release a new version of one of my apps and want to send a mail to all payed users.
Which mailing service is best to use? If I am not going to use my own email service because it will be blocked as a spam mail for sure in no time.
I need to send approx. 27000 mails … so what’s are you guys using?

I’ve made only positive experiences with
I even use it in one of my Apps to send mails to my users.