You can leave messages for your offline Skype contacts using instant messages or voice messaging. The instant messaging function is activated by default for all Skype accounts. The voice message system, however, must be configured by the user. Therefore, if your contact is offline and has not set up voice messaging, you will not be able to leave a voice message for him.

Instant Message Delivery Schedule

When you send an instant message to an offline contact, the message will not be delivered until both you and the contact are online simultaneously. Therefore, this may not be a good way to leave an urgent message. If, on the other hand, you always leave your Skype account online regardless of whether or not you are present, you can type the message and it will be delivered once your contact goes online.