Why Outlook, Hotmail and Live return 250 Mail queued for delivery, but they never deliver it? [duplicate]
Solution 1:
It's because of Microsoft's SmartScreen.
You gotta be in concordance with these topics:
- Setup a SPF record
- Setup DKIM
- Setup a DMARC record
- Setup a reverse DNS record
- HELO must be a host name not an IP
- Make sure that your IP is not on a blacklist
- Use a static IP address for your server
- Sign up for JMRP and SNDS
I've followed this article, which solved the same problem you're having.