[stevenicr]

I've run into similar recently with delivering to our own company's email boxes from our own server - company uses office365 / msoft business(?)

after jumping into dkim spf and all that, I can get delivered from our server to gmail.. but not to the company outlook boxes.. tried to get [third party corporate IT] to whitelist the ip or domain - they cant find receive attempts in logs..

back and forth, showing screenshots with timestamps, paying stupid money per hour to [NotNaming].. get told that well their msoft thing depends on AWS as a middle man and it is hardcore about spam stuff and if that's the problem it will take a ton of 3 team digging?

Giving up - now trying to find a way to have the server send an email to gmail and then forwarding to company's office365 - maybe, I dunno yet.

[fragmede]

if corp IT isn't seeing the connection attempt then some thing is blackholing the traffic. If the IP it's being sent from was caught sending spam anytime in the past (like even decades ago) it might be on a list. check via https://mxtoolbox.com/

There's also https://sender.office.com/ for o365.

The other question is how far is it getting before getting blackholed. if you're lucky "mtr -P 587 -T smtp.office365.com" from the company email server from might tell you who down the path is actually dropping the packets.

If there's budget for it, you can run a VPS in Azure and send it through that, connecting to 587 which is authenticated (25 is blocked), or use Sendgrid/similar that partners with Microsoft.

[internet1776]

Regulators need to do their job well instead of turning blind eye. Email is critical infra. for communication. These top players can't have monopolies on all communication.