utf-8のメールをmail.gemを使って送るとWARNINGが出る。 Non US-ASCII detected and no charset defined. Defaulting to UTF-8, set your own if this is incorrect. 明示的にcharsetを指定すればOK. # coding: utf-8 require 'rubygems' require 'mail' mail = Mail.new do to 'foo@example.com' subject 'テスト' body 'テストメール' end mail.charset = 'utf-8' # It's important! mail.delivery_method :sendmail mail.deliver