In Restore the Send a message link in users' profiles in the Your suggestions to make Amara great board I explained why it is so important for collaborative subtitling to be able to message fellow subtitlers, even if they don't belong to a team.
However, the URLs of Send a message links for all participants listed in any team member list seem to have the following form:
I.e. there is nothing team-specific about these URLs.
So, until Amara developers hopefully restore the Send a message link in all users' profiles: