Configuring SMTP Relay

Email has never been as simple as most people think it is. But if you need to connect a cloud application or an office photocopier to your organization email, SMTP relay can be pretty easy to set up--if you know how!
EXTRA CREDIT:
- SPF is only one of the two ways used to validate an email's source. The other method is DKIM. That's typically set up on the central mail server, so relaying through your organization's server allows the correct signature to be added.
- SPF and DKIM together are used as part of DMARC, which allows your organization to tell others how to deal with any email that claims to be from your organization but doesn't pass the validation checks.

[@TheWhiteRose-JunaidButt]

you have a wonderful personality you should make more videos teaching

[@NextDoorNetAdmin]

Thank you! I definitely plan to keep going. :)

[@JavierDiaz-zh2jo]

Hi,
Comcast and some other ISPs are blocking port 25, and the SMTP authenticators will be removed from Office 365. Do you know how to get around this port 25 issue?

[@NextDoorNetAdmin]

I do! Use a business connection. :)
Not to be glib about it, but residential connections often have port 25 blocked in order to combat spam being sent from unaware customers infected with malware. Customers accessing their remote email accounts will usually use a different port--sending directly to port 25 (with or without STARTTLS) is indicative of a server-to-server (relay) connection.
Conversely, since a business connection is expected to be running business applications (including email servers), all ports are generally left unblocked. Since you would need a static IP to add into the SPF record to permit the relay, that's also something typically available on a business connection.

[@JavierDiaz-zh2jo]

@@NextDoorNetAdmin Sorry to say, Comcast in Florida is blocking port 25, even for businesses (which is why I asked). Many companies are dealing with this. To get around it, I set up an SMTP relay server with postfix. It connects to Office 365 using TLS and an account with SMTP authentication enabled.

[@NextDoorNetAdmin]

@@JavierDiaz-zh2jo Ouch! That boggles my mind, honestly. Business connections should be unfiltered, in my mind--it's one of the main reasons to even get a business connection in the first place!
I'm going to guess that switching ISPs is likewise not a feasible option. If so, then I would honestly next look at ways of proxying the connection. First thing I would try is probably setting up an SSH tunnel to another endpoint where port 25 isn't blocked. If you had a way to SOCKSify the outbound connection, so much the better--you could use dynamic port forwarding instead of local port forwarding. But I'm afraid that I don't have a ready-made solution at hand for that problem... just ideas that would need more work.