FreeBSD upgrade on production server

[SUPPORT]

> Hello everybody,
> 
> I wish to upgrade my production firewall / mailserver / DNS server from
> 4.3 to 4.8. The simplest way seems to be use of CVSUP. OK, but...
> 
> Is it safe ? What should I backup ? There is running well-configured
> sendmail - are there some changes in its configuration between
> versions 8.11.3 used in FreeBSD 4.3 and 8.12.8p1 used in
> FreeBSD 4.8.
> This is my only mailserver and I don't have an secondary
> if something fails...
> 
> Please, advice if you have some know-how :-)))
> 
> Peter Rosa