Share Outlook contacts with another user on Office365 but NOT within same organisation


I have a client who is on Office365 and wants to access and edit/delete etc... the contacts on another client's mailbox who is also on Office365 but not on the same organisation, ie doesnt show up on the GAL.
How do i go about setting this up? what details do i need from the client who is sharing?

DominicIT ConsultantAsked:
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Vasil Michev (MVP)Commented:
You cannot share contacts cross-tenant.You can send them via Outlook but that's a one-off operation and not anywhere close to a sync.

One possible solution is to setup an SharePoint site with a Contact list and add the external user as Guest contributor. Not possible via Outlook/OWA though, as the O365 Groups/Teams do not expose Contacts functionality, so only SPO list will be an option. Similarly, you can create a regular user account instead of using a Guest user, but that would require a license.

Another option is to use some tool to syncronize the contacts/objects between the two tenants. Galsync is usually the tool we recommend for that.
DominicIT ConsultantAuthor Commented:
Hi Vasil - Thank you. I am surprised about the limitation here as MS seem to be doing a lot to enable collaboration. Anyway, apart from trying the above, i was also thinking of maybe getting another account setup on the external Client's organisation and then enabling sharing of contacts with the new mailbox and then finally setting up that mailbox on the internal client's Outlook so they can see the contacts but not any other data. You see we only want access to contacts , not visibility of mail/calendar. So at least this empty mailbox which exists within the other persons organisation can be setup as an Exchange account and have the shared contacts appended to it.

Would that work?
Vasil Michev (MVP)Commented:
If he has a mailbox, he will be able to see the full GAL and free/busy info for every person in the company (unless you have changed the Default level). I guess you can use some programmatic solution, such as EWS based script to copy/export the contacts from one mailbox to another. Glen has a module for such operations here:
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DominicIT ConsultantAuthor Commented:
Hi Vasil

If i create a mailbox on the same organisation as the person who is sharing their contacts (Call them Person A) and call it sharecontacts@.... I then share Person A's contacts with sharedcontacts@... which will work because they show up in the GAL. I then, add the sharedcontacts@ mailbox to the Outlook from the person in the external organisation (Person B). That way, Person B has an indirect route to the contacts without having to see the email and calendars of the Person A.

I hope this was clear, its a little less elegant when trying to write it then say it!

Vasil Michev (MVP)Commented:
it is, but you cannot restrict him to only be able to use the shared Contacts. You have to add the sharecontacts@ mailbox directly in Outlook (as additional account), you cannot just add the folder. Which in turn means he will be able to see the GAL, other people's free/busy info and so on.

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DominicIT ConsultantAuthor Commented:
Hi Vasil - We will be adding it as a full mailbox - And yes the GAL can be potentially seen but i usually configure Outlook Address Book to hide the GAL in the available contact lists. In theory Person B could still get to it but its just one user and she is not going to fiddle - It doesnt really matter if the GAL can be seen.
Now that i have confirmed with you that this can be a workable solution , i think we can close this case
DominicIT ConsultantAuthor Commented:
Thanks for confirming.
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