# Configure server host and user credentials if needed.
	fun set_outgoing_server(host: String, user: nullable String, pwd: nullable String): nullable CurlResponseFailed
	do
		# Check Curl initialisation
		if not self.curl.is_ok then return answer_failure(0, "Curl instance is not correctly initialized")

		var err

		# Host & Protocol
		err = is_supported_outgoing_protocol(host)
		if not err.is_ok then return answer_failure(err.to_i, err.to_s)

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

		# Credentials
		if not user == null and not pwd == null then
			err = self.curl.native.easy_setopt(new CURLOption.username, user)
			if not err.is_ok then return answer_failure(err.to_i, err.to_s)

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

		return null
	end