Subscription license is a paid and fully-functional license that expires at the end of the subscription term which is 1 or 3 years from the contract start date (depending on the subscription length).
After the license has expired, you will have a grace period which equals 1 month since the expiration date. During this period, the program functionality will not be limited by any means. After this period, processing of all mailboxes in all organizations will be stopped; scheduled jobs will be terminated with failure. In both cases, a notification message will be shown to notify you that your license is either about to be expired or has expired.
The restore abilities will continue to function regardless of whether your license has expired or not.
If your subscription license has exceeded its limit by up to 10 mailboxes or up to 10% of the license count (whichever is greater), Veeam will allow you to additionally process no more than 10 mailboxes or 10% of the license count.
If exceeded by more than 10 mailboxes or more than 10% of the license count (whichever is greater), you will be able to continue to process these 10 (or 10%) extra mailboxes according to the FIFO queue logic (that is, "first in - first out"); no more additional mailboxes will be processed.
The grace period in this case equals 1 month. After this period, processing of excessive mailboxes (in FIFO queue) will be stopped; no more extra mailboxes will be queued for processing. The corresponding messages will be displayed in the UI and written to the log.
The restore abilities will continue to function regardless of the grace period state.