^From \S+\s+\S+\s+\S+\s+\d+\s+\d+:\d+:\d+\s+\d+
+ is a suffix that means "one or more of the previous"
\s is any whitespace char (tab and space in this context)
\s+ is a sequence of one or more whitespace chars
\S is any non-whitespace char
\S+ is a sequence of one or more non-whitespace chars, call it a word
\d is a decimal digit char
\d+ is a one digit or multidigit decimal number
: is a plain colon
Eudora .mbx file example: "From ???(_at_)??? Mon Feb 23 16:58:32 1998"
1. "From "
2. Three words. ???(_at_)??? Mon Feb
3. One number. 23
4. A word consisting of three numbers separated by colons. 16:58:32
5. One number. 1998
-- SP
