alt Hacker Newsoutlook.com and O365 are horrible to deliver to. We regularly get issues where we sent an email it was accepted by O365 but was never delivered to the mailbox. We have one person working at least half the time on resolving stuff like that. And that's from a respectably maintained SES egress with good reputation, DMARC, DKIM configured.
Replies
I have a small client with a large email list who wants to switch from once a month constant contact newsletters to sending them through SES with a self-hosted Sendy instance. This seemed like a reasonable way to save $10k a year or so. I haven't used SES before for anything. I have run an email server for 30 years and had occasional blacklist headaches, but it's not used for mass mailing of that sort... it's usually several years between problems. Is this a terrible idea to switch, even if it's off a "managed" SES dedicated IP? I don't want to switch them and find out no one on Outlook is getting their mail.
What's the nature of your operation? If they're not giving you money then you're within your rights to say "sorry, don't use outlook"
Funny, they have no problem handling mail for essentially every Fortune 500 company and others large and small.
It's always people self-hosting mail on a shared server in Moldova (because they think it makes them cool) that are complaining.
There is a trick. Sign up with them, configure custom domain, but don’t set your MX records. On your MTA, route mail that goes to Outlook/Hotmail to go through their MSA with your Outlook credentials and headers stripped as if submitted directly by user. Outlook gets mail through their own MSA it trusts, rest of the world talks to your mail system directly. Replies still go to your MXes.
I haven’t productionized this setup (I send maybe a dozen emails a year) but it worked for me ad hoc a couple years back, when I had to send a mail to an Outlook-hosted address and they blackholed everything I tried to send while 250 OKing me.