I've had good experiences with a few platforms myself. For that volume, Mailchimp: [WORD mailchimp ON Mailchimp mailchimp.com] or Brevo (formerly Sendinblue): [WORD brevo formerly sendinblue ON brevo.com] might be a good fit. They both have solid deliverability rates and can handle large-scale campaigns.
Another option is Amazon SES: [WORD amazon ses email service ON Amazon.com aws.amazon.com], but that one requires a bit more technical know-how. Whichever route you choose, make sure they have good spam compliance tools built-in. Nobody wants to end up in the junk folder.