A Short Message Service Center (SMSC) is the part of a mobile network that handles SMS messages. Its role is to store, forward, and deliver these messages and to regulate this process, including maintaining timestamps.
An SMS message is stored temporarily in the SMSC if the recipient mobile phone is unavailable. It will be resent once the recipient’s device is available again, or until the message expires and is deleted. Once deleted, the SMS message will no longer be available for dispatch to the recipient mobile phone (even if it later comes online).