I run VoIP PBXes and they occasionally need to send an email, usually for voicemail to email but occasionally for other alerts.
By default they just send straight to the internet, sending from pbx@pbx.domain.name, forward and reverse DNS mapping back to their own addresses, etc. but no other setup.
This works perfectly fine with Gmail and Gsuite accounts, but Office 365 occasionally decides it hates one of our servers. Even if the client has the sending address whitelisted, it still just gets hard blocked for no apparent reason.
Gmail, I can fire up a telnet session right now and send myself an email from my home IP address just typing raw SMTP commands in to a console. It's going to work, and unless I'm spoofing a real email address it's not even going to end up in spam.
I run VoIP PBXes and they occasionally need to send an email, usually for voicemail to email but occasionally for other alerts.
By default they just send straight to the internet, sending from pbx@pbx.domain.name, forward and reverse DNS mapping back to their own addresses, etc. but no other setup.
This works perfectly fine with Gmail and Gsuite accounts, but Office 365 occasionally decides it hates one of our servers. Even if the client has the sending address whitelisted, it still just gets hard blocked for no apparent reason.
Gmail, I can fire up a telnet session right now and send myself an email from my home IP address just typing raw SMTP commands in to a console. It's going to work, and unless I'm spoofing a real email address it's not even going to end up in spam.