They dont tollerate it they go to somewhere they can use pop3 and get their mail on another machine maybe pull it in off a mobile phone or plug in to some wireless network outside the affected zone.
If you use fetchmail, they won't be able to do that. Their mail will have been moved from their ISP's mail server to the SME server which is down.
As I've said repeatedly - if their mail must be delivered to the ISP rather than your SME server, just configure their POP3 (or preferably IMAP) clients to directly access the mailbox at the ISP.
Alternatively, if you always know better than us, just do what you know to be best and leave us alone.
