I’ve searched this forum about SNDS and founded a couple of threads (but they are already closed) of people that has faced this before.
I started to get some undelivered errors from outlook when sending emails to hotmail or companies that have their email services managed by outlook due to my mailinabox server IP being blocked.
After requesting to whitelist my IP, I got a denial and I was referred to this support page.
After registering on SNDS (which includes JMRP), I’ve replied to the initial support ticket (which can be also accessed from the SNDS site) and it seems now I’m going to be whitelisted (but have to wait 24/48h to confirm).
I think this is useful information and I’d have loved to find it in a last step on the setup guide, something like a “What’s next…” section with indications to this and other useful external settings that the community may have founded. That way we will speed up the set up of a server compatible with 99.9% of the SMTP servers out there and save a bunch of hours to Mailinabox users.