One of our users is repeatedly being asked to add email senders to his safe list in Outlook on the web. He sees a standard message like this across the top of his screen whenever he receives an email from a new sender:
He has been clicking the 'trust content' link (and therefore adding senders to the list) for about three months since the issue apparently started but has now run out of room in that safe list because he has approx 1000 entries.
Rather than simply increase the space in this list (if that's even possible), how can I establish why he is having to do this with every person/business that writes to him the first time. In some cases there are attachments or links in those emails but other times they just contain text so I'm not sure what Microsoft believes it has blocked. I don't think this is an issue with safe attachments or safe links, the mails usually arrive in his Inbox as opposed to Junk and he hasn't set any junk email filters.
We have a Microsoft 365 Standard package plus Defender for Office 365 Plan 1 subscription. No one else in our organisation is facing this issue on every new senders email they receive which suggests the problem isn't being caused by a global setting.