Forum Discussion
SMTP Relay in Exchange Online
Currently we run Exchnage 2019 hybrid. We have not moved our MX records to Exchange Online yet for specific reasons so all mail flow is through Exchange 2019. That said, nearly all user/shared mailboxes have been migrated to Exchange Online. We also have many devices using SMTP relay through Exchange 2019 on-prem (printers etc.) to send mails mainly internally but also some externally (UPS devices for example). Most of these devices do not support authentication so we have setup a mail connector that uses an IP whitelist on Exchange 2019 to handle this.
If we get rid of the hybrid and move to Exchange Online what options would we have for this type of unauthenticated relay?
This has methods you can use, if its low volume, and you can use port 25 on your ISP, this method would work for your non-authenticated.
Keep in mind that Microsoft doesn't want people using Exchange Online for bulk mailing. If you're going to bulk mail transactional emails, you will need to look into a different product (Sendgrid, AWS SES, Mailgun, Azure Communication Services, etc.). There are some hard limits coming next year that will impact bulk mailing with Exchange Online.
