# Execute Mail request with settings configured through attribute
	fun execute: nullable CurlResponseFailed
	do
		if not self.curl.is_ok then return answer_failure(0, "Curl instance is not correctly initialized")

		var lines = new Array[String]

		# Headers
		var headers = self.headers
		if not headers.is_empty then
			for k, v in headers do lines.add "{k}{v}"
		end

		# Recipients
		var all_recipients = new Array[String]
		var to = self.to
		if to != null and to.length > 0 then
			lines.add "To:{to.join(",")}"
			all_recipients.append to
		end

		var cc = self.cc
		if cc != null and cc.length > 0 then
			lines.add "Cc:{cc.join(",")}"
			all_recipients.append cc
		end

		var bcc = self.bcc
		if bcc != null and bcc.length > 0 then all_recipients.append bcc

		if all_recipients.is_empty then return answer_failure(0, "There must be at lease one recipient")

		var err = self.curl.native.easy_setopt(new CURLOption.follow_location, 1)
		if not err.is_ok then return answer_failure(err.to_i, err.to_s)

		err = self.curl.native.easy_setopt(new CURLOption.mail_rcpt, all_recipients.to_curlslist)
		if not err.is_ok then return answer_failure(err.to_i, err.to_s)

		# From
		var from = self.from
		if not from == null then
			lines.add "From:{from}"

			err = self.curl.native.easy_setopt(new CURLOption.mail_from, from)
			if not err.is_ok then return answer_failure(err.to_i, err.to_s)
		end

		# Subject
		var subject = self.subject
		if subject == null then subject = "" # Default
		lines.add "Subject: {subject}"

		# Headers body
		var headers_body = self.headers_body
		if not headers_body.is_empty then
			for k, v in headers_body do lines.add "{k}{v}"
		end

		# Body
		var body = self.body
		if body == null then body = "" # Default

		lines.add ""
		lines.add body
		lines.add ""

		err = self.curl.native.register_callback_read(self)
		if not err.is_ok then return answer_failure(err.to_i, err.to_s)

		var content = lines.join("\n")
		err = self.curl.native.register_read_datas_callback(self, content)
		if not err.is_ok then return answer_failure(err.to_i, err.to_s)

		var err_resp = perform
		if err_resp != null then return err_resp

		return null
	end