Creating a Google Group for the WebServices Team (Option A) is the most efficient approach to centralize both Identity and Access Management (IAM) permissions and email distribution. Google Groups allow for the assignment of IAM roles to the group, which then apply to all members of the group, simplifying permission management. Additionally, Google Groups can be used as email distribution lists, addressing the need for centralized email distribution. Creating a G Suite Domain (Option B) or a new Cloud Identity Domain (Option C) would be overkill for this purpose, as it involves setting up an entirely new domain, which is not necessary for centralizing permissions and email for a single team. Creating a new Custom Role (Option D) would allow for customized permissions but does not address the email distribution requirement, making it an incomplete solution.