I never found out the cause of this, but have now figured it out. Here's what MS Outlook had for me this morning:
I'm now receiving three copies of university emails. This follows the renewal of my honorary professorship.
Either I've been added to a database three times or I've been added to three different database. Email addresses aren't intersected before emails are despatched, so I'm seeing three copies of stuff.
I've asked the IT help desk people if they can fix it. They acknowledged my email (only one copy!) but noted "We are experiencing a high volume of queries at the moment and we'll get back to you as soon as we can."
I suspect this is a signature that's automatically appended to all their emails.