If there is an issue with the archiver and its connectivity, there are a number of ways to maintain the performance of the appliance, dependent on the configuration.
If the archive has been set up to archive from a Journal Mailbox, the emails will back up within the journal folder until the connection to the archiver is reestablished. The stockpiled information will subsequently transfer once the appliance is reconnected.
If the archive is arranged to pull from SMTP servers, usually there are rules in place that regulate how long they will retain emails. For example, if connection to the archiver has failed, the SMTP server may only hold on to emails for 72 hours before data is erased. Upon re-connection, the data will automatically archive itself, as with a Journal folder.