Mailbox is shown, but not the mails

Summary

Sometimes a mailbox is shown, also in the newsfeed, but you can't access the emails.

In this case, the user is part of a workgroup, but not a BIEB. The support has named this as the reason for not being able to access the emails.

Steps to reproduce

Probably like this: You need to be a FS but not a BIEB. (BIEB-Quiz not solved yet.) You need to be appointed as manager for a workgroup, so you can handle the emails. Klick on the letter-Sign to access the mailbox. Klick on the workgroup-related mail address. Are emails shown?

What is the current bug behavior?

The mailbox is shown, also in the newsfeed, but you can't access the emails.

What is the expected correct behavior?

Sometimes a mailbox is shown, also in the newsfeed, AND you can access the emails - even though you aren't a BIEB yet.

Relevant error messages and/or screenshots

(Include any relevant error messages or screenshots here)

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)