I have multiple domains hosted on a VPS. Hotmail seems to reject email from certain domains (it does not even arrive in the spam folder), but accepts email from other domains (on that same VPS). What could be the problem? I already set up spf and DKIM. I guess this could not be a problem related to blacklisted ip's since all domains point to the same ip address. What could be the reason that not all mail is received by hotmail (it works for gmail)?
Thanks
Your domain accumulates reputation scores managed by different organisations, which are mostly pretty hard to find out about. Smaller email hosts may be clients of external reputation scoring services. An organisation like hotmail probably runs it entirely themselves.
A likely one is that you might be running mailing lists where you haven't cleaned out the addresses which fail to deliver. Repeated failed deliveries will cost you reputation pretty quick.
Mostly it just comes down to making sure you follow best practices in every way you can think of. If you set up DMARC, you may get some clues in the reports from hotmail about what failed, but more importantly you can monitor what is failing to make sure you stop sending to invalid addresses.
There's a lot to learn here. It's quite likely to be more cost-effective for you to use a mail delivery service like sendgrid who will handle all the above for you.
