It occurred to me that Johnny C. Lam wrote in gmane.os.netbsd.devel.packages:
> I completely agree with you here.  This is why I suspected I may have to 
> push this type of script into the packages that use db4 instead, e.g. 
> cyrus-sasl2 (/usr/pkg/etc/sasldb), postfix (hash: maptype), cyrus-imapd 
> (/var/imap and /var/spool/imap mailboxes), etc.

Running the risk of suggesting something perpetually stupid here:

Would it be possible to teach these packages how to backup and restore their
databases?