Forum Discussion
Guest access issues
The difference in her email and account is the issue. The user has to sign in as the email invited. Can the user not be invited on user@company.company.com and get the email through that? Can an alias somehow be setup(not sure on the technical term there) ?.
You could get around this by inviting the user to a SharePoint site in the external tenant the person doing the inviting will get an email which can be forwarded to the user. The user can then use the link to accept the invite. The account will then be created in the external tenant. This would then allow them access to Team when logging in to your own teams and changing the tenant in the top right.
Long term it would be worth looking at merging the email and sign in, I have seen users have 2 domains assigned to the same account but beyond my ability to suggest how to accomplish that.