canvas-lms/app/messages/new_context_group_membership_invitation.email.erb

<% define_content :link do %>
  <%= HostUrl.protocol %>://<%= HostUrl.context_host(asset.group.context) %>/<%= asset.group.context.class.to_s.downcase.pluralize %>/<%= asset.group.context_id %>/groups/<%= asset.group_id %>
<% end %>
<% define_content :subject do %>
  <%= t :subject, "New Group Membership for %{course_or_account}", :course_or_account => asset.group.context.name %>
<% end %>

<%= t :title, "New Group Membership: %{group_name}", :group_name => asset.group.name %>

<%=
    case asset.group.context_type
    when 'Account'
      t :body_account, "You've been invited to join the group %{group} for the account %{account}.", :group => asset.group.name, :account => asset.group.context.name
    else
      t :body_course, "You've been invited to join the group %{group} for the course %{course}.", :group => asset.group.name, :course => asset.group.context.name
    end
%>

<%= t :details, "You can check out the group by clicking the link below:" %>
<%= content :link %>