fetchmail, when does one loose email?

[wsa <wsa3@xs4all.nl>]

I've been following the recent threads on fetchmail and i've been 
reading up on it but i'm  not quite clear on when one can loose mail.
Right now in fetchmailrc i have "set no bouncemail, antispam -1, 
batchlimit 50, keep" as defaults.
Fetchmail in my case fetches email of several pop3 servers from where it 
goes into exim and exim passes it on to icourer imap.
According to the man  page fetchmail  under --flush: " What you probably 
want is  the  default  set­ting:  if  you  don't  specify `-k', then 
fetchmail will automatically delete messages after successful delivery. "
So if i remove 'keep' from the defaults fetchmail will automatically 
delete messages from the pop server after successful delivery to my MTA, 
exim in my case, if one goes by the manual.
From this it seems  that even if the exim setup, or whatever MTA,  is a 
mess...fetchmail will not delete any mail because a delivery would 
simply not be succesfull. Yet there's  loads and loads of  people 
loosing email at one point or another due to a badly configured MTA.
In short, am i still at risk of loosing email even if i don't have an 
antispam filter in exim (so no error 571 will be send from exim to 
fetchmail).

cheers.