What happens to faxes if the e-mail server fails for a long time?

If the e-mail server fails, what should I bear in mind if fax messages are to be delivered to users via this e-mail server? 

The XPhone Server attempts to deliver fax messages to the e-mail server, e.g. Microsoft Exchange or IBM Lotus Domino Server, for five days. After five days, these fax messages are stored in the XPhone Server program directory in the subdirectory \UMS\Spool\Fax2Mail\NotSent. 
When the mail server is available again, you can copy the files it contains to the WORK directory on the same level. Now the faxes are delivered to the e-mail server.