Hi @Brendan Marsh ,
Are you using web mail or Outlook client?
If the issue occurred on Outlook desktop client, due to it occurred only recently, in order to avoid the interference of corrupted profiles, it's suggested to create a new Outlook profile and readd your account to check(Control Panel>Mail>show profiles>Add>readd your account)
Besides, if you actually have issue on your web mail, it may be more related to your account itself, I have searched a lot about it, due to you could receive mails in Junk folder, it's suggested to first change the junk option and check the forwarding settings of your account in web mail(settings>view all settings>Junk/forwarding) to check. I have also found a related article : Fix Outlook. com email sync issues, please try to troubleshoot your issue as mentioned above, if that's invalid, please understand here we mainly focus on general issues on Outlook desktop client, in order to solve your account issues better, it's suggested to contact account support .
Hope your issue would be resolved soon.
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