This week I noticed strange contacts in my contact list in Outlook. Contacts I'm sure I did not create myself, like Facebook notification mails, the Service Engineer at Microsoft that handled a support ticket, update mails of Yammer and the mail address of a Office 365 Group.
I don't know why this happens and I don't know how I can stop it!? I checked every mail app I use (Outlook Desktop, Outlook Web, W10 Mail and Calendar), but can't find an option to change.
Afaik there is no such option in Outlook or OWA that I'm aware of. Haven't used the W10 client, so I cannot speak for that, mobile clients are another thing that comes to mind. Apart from that, check for any add-ins that might be doing this. You can also enable auditing on owner actions and see how the contact item gets created.
Are they in the Contacts folders or another folder?
If you see them when you search for names, it's probably the new Other Suggestions feature which shows you addresses from recent messages. They aren't actually saved contacts, but a version of the autocomplete list
So, the audit logs shows 66 actions in May of contacts being created by some app. I can only see this in my audit log:
Angela Viesse on Yammer
Michiel van den Broek
The email from Angela Viesse was received on 26-5-2018, Outlook says at 00:02. So about 10 minutes prior to the contact being created. As it happens to be, I can tell for sure I was not checking my email at that time. And I also know for sure that my computer was turned off, so it isn't done by any add in in Outlook Desktop. The audit log says WebServices, so it has to be some app connected to my account.
I also checked Outlook for the contacts. I notice a different icon:
My other contacts have the "normal" business card icon.
I can't remember having any app accessing (and editing) my contacts. And 95% of my apps are from Microsoft services. So where can I check which apps are accessing my account?