If your sending from your server / own built application, the best way to do it would be to set up phpmailer and use an SMTP sending service otherwise your server ip could get blacklisted.

If your using Wordpress, mailpoet is quite useful and you can pop your SMTP settings straight in from a service like SendinBlue or Mailjet

Hi there,

I would recommend carefully going through the DigitalOcean publicly here:

https://www.digitalocean.com/legal/acceptable-use-policy/

The main points are:

You must comply with the laws and regulations applicable to bulk or commercial email in your jurisdiction. In addition, your bulk or commercial email must meet the following requirements:

• You must have a privacy policy or similar disclosure posted for each domain associated with the mailing;
• You must have the means to track anonymous complaints;
• You must not obscure the source of your e-mail in any manner;
• You must post an email address for complaints (such as abuse@yourdomain.com) in a conspicuous place on any website associated with the email, and you must promptly respond to messages sent to that address;
• Your intended recipients have given their consent to receive e-mail via some affirmative means, such as an opt-in procedure, and you can produce the evidence of such consent within 72 hours of receipt of a request by the recipient or DigitalOcean;
• You must use reasonable means to ensure that the person giving consent is the owner of the e-mail address for which the consent is given;
• You must include the recipient’s e-mail address in the body of the message or in the “TO” line of the e-mail; and
• You must honor revocations of consent and notify recipients of the same.

As an alternative, I could suggest using an SMTP provider like SendGrid for example which specializes in SMTP services.

Regards,
Alex