Hello,
This has been an ongoing issue for a week.
https://www.reddit.com/r/Outlook/comments/1w67w2t/is_anyone_else_unable_to_block_domains_from_junk/
https://learn.microsoft.com/en-us/answers/questions/5993215/how-to-fix-not-saving-settings-in-undoing-block-se
Via https://learn.microsoft.com/en-us/answers/questions/5988478/cannot-save-changes-to-junk-email-safe-or-blocked
Thank you for your patience, Ed. I have consulted with our Tier 2 team and they confirmed that this is a known issue affecting some Outlook.com users. We have received multiple reports of customers being unable to save changes to their Safe Senders or Blocked Senders lists and receiving the message: "Couldn't save changes. Something went wrong. Please try again later."
Our engineering team has already identified the root cause and a fix is currently being rolled out to affected accounts.
I hope this information helps. If you have any more questions, don't hesitate to reach out. Wishing you good luck!
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