Wade suggested to Robert,
| Perhaps something like the following?
| cat oldmailfile | formail +1 -ds procmail
The +1 is for breaking up digests, where you don't want the digest's own
envelope stored along with the component articles.
formail -s procmail < oldmailfile
is the basis of what Robert needs; Anbrew's pointer to the man page will
explain the rest.
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