Bulk mailing it's a process, it's not just an smtp and send.
Cleaning list from non existent emails (bounces), remove generic emails like info, contact...
Cleaning from spam traps
Warm-up your servers
Create your suppression list to exclude unsubscribers and complainers
Segment your list openers/clickers and interests.
Make them double opt-in, it's your active list.
There are some mailing services here in BHW marketplace, or you can create your server or servers using PowerMTA with Mailwizz or Mumara
Good luck