This depends on the version of Skype you are using to send the instant message.

• If you are using Skype for Mac 2.8 or lower, both you and the recipient need to be signed in to Skype for the message to be delivered.
• If you are using Skype for Mac 5.0 or higher, instant messages you send will be saved by Skype and delivered as soon as the recipient signs in, even if you are not signed in.

Messages sent using Skype 5.0 or higher are saved by Skype for 30 days after the message is sent. During this time, any saved messages will be delivered if the recipient signs in using Skype 5.0 or higher. If the recipient signs in using Skype 2.8 or lower, saved messages will not be delivered.

Because instant messages are saved with Skype 5.0 or higher, if you sign in to Skype 5.0 or higher on a different computer, instant messages you have sent or received on one computer in the last 30 days will be copied to the other, enabling you to automatically synchronize your chat history between computers.

Saved messages are stored by Skype in encrypted format and will be deleted after 30 days. For more information on how Skype manages personal data, please refer to section 13 of the Skype Privacy Policy.