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You need first to make sure that your email provider will allow you to send this amount of emails, because a lot of providers have low limits for the outgoing messages. You can check this with your mail provider and once you know the limit, you can automate the process or use any third-party bulk mailing software to send your emails.
Also you need to make sure that your mailing list is OPTED-IN, meaning that all the email addresses in it have permitted you to send them emails.
Feel free to ask if you have any questions.
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