Any problems sending a lot of emails with rails like this:
@members = Members.all @members.each do |m| MemberMailer.message(@message, m).deliver end
The major problem would be if you are a user and somehow when you signup or try to sendo those emails through some action, the server could return a timeout response, if you have a lot of users. What I recommend you to do is, put all mailers call inside a worker like sidekiq or sucker_punch. it will help a lot with rake tasks in and other piece of code in background jobs.
hope I have helped you.
nice day