using sendgrid4r to create a custom ActionMailer delivery method that uses the sendgrid v3 api

sendgrid_sender.rb

require 'mail/check_delivery_params'
require 'sendgrid4r'

class SendgridSender
  include ::Mail::CheckDeliveryParams

  def initialize(options = {})
    @api_key = options[:api_key]
  end

  def factory
    SendGrid4r::Factory::MailFactory
  end

  def client
    @client ||= SendGrid4r::Client.new(api_key: @api_key)
  end

  def deliver!(mail)
    check_delivery_params(mail)

    per = factory.create_personalization(
      to: mail.to.map do |email|
        factory.create_address(email: email)
      end
    )

    html = factory.create_content(
      type: 'text/html',
      value: mail.body.to_s
    )

    from = factory.create_address(
      email: mail.from.first
    )

    params = factory.create_params(
      personalizations: [per],
      from: from,
      subject: mail.subject,
      content: [html]
    )

    client.send(params: params)
  end
end