External Users and Contacts - improve the way relationship is handled
For some purposes Microsoft intends a Contact be used, for others an External user. Some other ideas I have seen people post may be based on a misunderstanding of this, but Microsoft have not helped.
Creation of a Contact is supposed to be a conscious decision by an Administrator.
Meanwhile an External User is created by the system to handle shares with people not on the system.
Many who have had problems do not realise, but if they create a Contact first, and THEN share with that 'Contact', Microsoft sets up a matching #EXT# (external user) and everything is OK.
The problem is that a lot of people have done some sharing first, before they realise an #EXT# user is not adequate for all purposes. If they try to create a matching Contact AFTERWARD they get an error:
'The proxy address "SMTP:email@example.com" is already being used by the proxy addresses or LegacyExchangeDN of "somebody_blah.com#EXT#" '
In other words they are punished by the system for doing things the wrong way round. Their only option is to delete the #EXT# user, create a contact, then do all their shares again, finally creating an #EXT# user which matches the contact.
PLEASE MICROSOFT: instead of this error give something like:
'The proxy address "SMTP:firstname.lastname@example.org" is already being used by the external user "somebody_blah.com#EXT#" - are you trying to create a matching contact?'
Then you could click 'yes' and carry on.
You can already create a contact, then an external share to that contact and get a matching #EXT# user.
But you cannot do it the other way around, even though it is likely that external shares will happen before people realise a Contact is needed.