Outlook Reminders showing other people's reminders

I recently upgraded a colleagues Outlook from Outlook 2010 to Outlook 2016. This colleague has a lot of shared calendars with other colleagues.

What is happening, is this colleague is now receiving the reminders that other colleagues have set on their calendars. So they're receiving around 15 - 30 reminders every 5 to 10 minutes.

I initially thought this was down to the delegate settings set on people's Outlook accounts that they were connected with, but none of the settings where marked for my colleague to receive them. This is an example of what settings I have set under delegates:

I then thought it might be down to the permissions set on each calendar but when I went in and looked I couldn't find any settings under the calendar(s) themselves with an option to switch off the reminders for that particular person:

I can't seem to find a fix for this.. has anybody else come across this issue and know how to stop it from happening? Removing the shared calendars completely is not an option as everybody requires access to each others calendars.

By default, reminders are only shown for mailboxes added in the Account Settings section of Outlook.

If this users only needs to view the calendars and not the actual mailboxes, they'll need to remove the extra mailboxes from Account Settings, and instead add the calendars in the Calendar section using Open Calendar or right-clicking on a Group and selecting Add Calendar.