If I understand correctly, the question is about Canada Post employees. Again, that's a question for Canada Post.
What I can offer as a general explanation is that a bilingual federal office does not require all staff in that office to be bilingual. However, all services must be offered to the public in both official languages. An institution can organize its operations in various ways, including through recruitment and language training, to ensure that office staff have sufficient bilingual capacity to meet its obligations to serve the public in both languages.