Currently, when the access to a Conversations Inbox is restricted to only allow specific teams and users (“Inbox settings” > “Access” > “Select users and teams who can edit”), it’s only possible to tag users (i.e. “@mention”) into a conversation’s comments who are listed as the “Primary team members” of a User Team. This means users listed as “Additional team members” in the team cannot be tagged in conversations comments.
The issue is that HubSpot users are expecting that they should be able to @mention any team member of the assigned team to their conversations inbox. However, this is only working for Primary team members. Additional team members do not appear as options when mentioning users in an inbox. This makes it difficult for partnering teams to coordinate with each other to best resolve customer conversations.

