I've been running a private mailserver for myself and a couple of friends since 2002. I hit a similar issue with Microsoft last year. I route outgoing mail to

I've been running a private mailserver for myself and a couple of friends since 2002. I hit a similar issue with Microsoft last year. I route outgoing mail to hotmail.com, live.com, outlook.com and msn.com domains via email-smtp.us-east-2.amazonaws.com. I started doing this when I noticed a large portion of e-commerce email I was receiving originated from amazon vms and they clearly had no deliverability issues. The ability to do this is a paid-for service, and needs to be configured appropriately. I was expecting to have to pay for a VM when I set out to do this. However, it turns out you do not need that - you can just configure the SMTP forwarding without needing to purchase any other products, and the cost for this is a few cents per 10k emails, which I can see would be significant for commercial services and/or spammers, but for a private mail server essentially means I will never have to pay. Amazon go to great pains to maintain deliverability for those servers, so you don't have to. I don't really see a problem with adding one extra SMTP hop to outgoing emails tbh, but as no-one other than Microsoft has (to date) a permanent IP block ban with no recourse whatsoever policy, while I've had transient issues with most other big providers at one time or another, those four Microsoft domains remain the only destination I have to route this way.