function messages_new_message( $args = '' ) {

	// Parse the default arguments.
	$r = bp_parse_args( $args, array(
		'sender_id'  => bp_loggedin_user_id(),
		'thread_id'  => false,   // False for a new message, thread id for a reply to a thread.
		'recipients' => array(), // Can be an array of usernames, user_ids or mixed.
		'subject'    => false,
		'content'    => false,
		'date_sent'  => bp_core_current_time(),
		'error_type' => 'bool'
	), 'messages_new_message' );

	// Bail if no sender or no content.
	if ( empty( $r['sender_id'] ) || empty( $r['content'] ) ) {
		if ( 'wp_error' === $r['error_type'] ) {
			if ( empty( $r['sender_id'] ) ) {
				$error_code = 'messages_empty_sender';
				$feedback   = __( 'Your message was not sent. Please use a valid sender.', 'buddypress' );
			} else {
				$error_code = 'messages_empty_content';
				$feedback   = __( 'Your message was not sent. Please enter some content.', 'buddypress' );
			}

			return new WP_Error( $error_code, $feedback );

		} else {
			return false;
		}
	}

	// Create a new message object.
	$message            = new BP_Messages_Message;
	$message->thread_id = $r['thread_id'];
	$message->sender_id = $r['sender_id'];
	$message->subject   = $r['subject'];
	$message->message   = $r['content'];
	$message->date_sent = $r['date_sent'];

	// If we have a thread ID...
	if ( ! empty( $r['thread_id'] ) ) {

		// ...use the existing recipients
		$thread              = new BP_Messages_Thread( $r['thread_id'] );
		$message->recipients = $thread->get_recipients();

		// Strip the sender from the recipient list, and unset them if they are
		// not alone. If they are alone, let them talk to themselves.
		if ( isset( $message->recipients[ $r['sender_id'] ] ) && ( count( $message->recipients ) > 1 ) ) {
			unset( $message->recipients[ $r['sender_id'] ] );
		}

		// Set a default reply subject if none was sent.
		if ( empty( $message->subject ) ) {
			$message->subject = sprintf( __( 'Re: %s', 'buddypress' ), $thread->messages[0]->subject );
		}

	// ...otherwise use the recipients passed
	} else {

		// Bail if no recipients.
		if ( empty( $r['recipients'] ) ) {
			if ( 'wp_error' === $r['error_type'] ) {
				return new WP_Error( 'message_empty_recipients', __( 'Message could not be sent. Please enter a recipient.', 'buddypress' ) );
			} else {
				return false;
			}
		}

		// Set a default subject if none exists.
		if ( empty( $message->subject ) ) {
			$message->subject = __( 'No Subject', 'buddypress' );
		}

		// Setup the recipients array.
		$recipient_ids = array();

		// Invalid recipients are added to an array, for future enhancements.
		$invalid_recipients = array();

		// Loop the recipients and convert all usernames to user_ids where needed.
		foreach ( (array) $r['recipients'] as $recipient ) {

			// Trim spaces and skip if empty.
			$recipient = trim( $recipient );
			if ( empty( $recipient ) ) {
				continue;
			}

			// Check user_login / nicename columns first
			// @see http://buddypress.trac.wordpress.org/ticket/5151.
			if ( bp_is_username_compatibility_mode() ) {
				$recipient_id = bp_core_get_userid( urldecode( $recipient ) );
			} else {
				$recipient_id = bp_core_get_userid_from_nicename( $recipient );
			}

			// Check against user ID column if no match and if passed recipient is numeric.
			if ( empty( $recipient_id ) && is_numeric( $recipient ) ) {
				if ( bp_core_get_core_userdata( (int) $recipient ) ) {
					$recipient_id = (int) $recipient;
				}
			}

			// Decide which group to add this recipient to.
			if ( empty( $recipient_id ) ) {
				$invalid_recipients[] = $recipient;
			} else {
				$recipient_ids[] = (int) $recipient_id;
			}
		}

		// Strip the sender from the recipient list, and unset them if they are
		// not alone. If they are alone, let them talk to themselves.
		$self_send = array_search( $r['sender_id'], $recipient_ids );
		if ( ! empty( $self_send ) && ( count( $recipient_ids ) > 1 ) ) {
			unset( $recipient_ids[ $self_send ] );
		}

		// Remove duplicates & bail if no recipients.
		$recipient_ids = array_unique( $recipient_ids );
		if ( empty( $recipient_ids ) ) {
			if ( 'wp_error' === $r['error_type'] ) {
				return new WP_Error( 'message_invalid_recipients', __( 'Message could not be sent because you have entered an invalid username. Please try again.', 'buddypress' ) );
			} else {
				return false;
			}
		}

		// Format this to match existing recipients.
		foreach ( (array) $recipient_ids as $i => $recipient_id ) {
			$message->recipients[ $i ]          = new stdClass;
			$message->recipients[ $i ]->user_id = $recipient_id;
		}
	}

	// Bail if message failed to send.
	$send = $message->send();
	if ( false === is_int( $send ) ) {
		if ( 'wp_error' === $r['error_type'] ) {
			if ( is_wp_error( $send ) ) {
				return $send;
			} else {
				return new WP_Error( 'message_generic_error', __( 'Message was not sent. Please try again.', 'buddypress' ) );
			}
		}

		return false;
	}

	/**
	 * Fires after a message has been successfully sent.
	 *
	 * @since 1.1.0
	 *
	 * @param BP_Messages_Message $message Message object. Passed by reference.
	 */
	do_action_ref_array( 'messages_message_sent', array( &$message ) );

	// Return the thread ID.
	return $message->thread_id;
}