Hey everyone! I'm trying to get some insights about replacing our on-premises Exchange server, which we mainly use as an SMTP relay for internal communications and some external emails to customers. It seems that this setup might not be the best choice moving forward, especially considering the future of on-prem Exchange. We're currently using O365 and Proofpoint, both of which have relay features, but I'm concerned about having every server that sends out emails needing to authenticate. Ideally, I'm looking for a solution that allows us to maintain an open relay within our firewall for forwarding SMTP mail externally. Has anyone gone through a similar transition or have suggestions? Thanks!
5 Answers
Postfix could be a solid choice here. It's free and open-source, plus it runs smoothly on a Linux server within your network. You can easily whitelist the internal addresses that are allowed to send out emails, and it can relay all your mail through the O365 send connector. Plus, it keeps logs if you need them.
Another alternative is to install the SMTP server role on a Windows server you have. It allows you to create a virtual SMTP server to handle relay purposes. Just keep in mind that the Windows relay role only supports basic authentication, which M365 plans to disable soon.
You might also want to check out SMTP2GO as another option for your needs.
We also use Postfix with Ubuntu and have implemented certificate enforcement to ramp up security. It's straightforward to set up and works well for what we need.
There are quite a few options out there. If you search for 'On-Premise SMTP server', you'll find a variety of choices like Xeams, Mail Enable, and MDaemon, to name a few.
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