I don't know if this will work for what you want (and it may not be the best solution, so I pray other, wiser monks will comment, so we both may learn), but this is how I have handled it in the past (with __DATA__ for testing, fields named as they were so I could verify the results quickly visually). Good luck in finding a solution. 
#!/usr/bin/perl -w
use strict;
use warnings;

my $multiline_seperator = "\n";
my ($fieldname, $fieldvalue, $line, %pkg);

while ($line = <DATA>) {

    # Lines following empty/space/astrisk-filled lines 
    #   assumed to be comments
    $fieldname = undef    
        if (($line =~ m/^\s+$/) or ($line =~ m/^\*+$/));
    chomp($line);

    # Assumes colons do not appear except in lines with field names
    if ($line =~ m/:/) {
        ($fieldname, $fieldvalue) = split(/:/, $line, 2);

        # Remove trailing spaces from field name,
        #   leading spaces from field value
        $fieldname =~ s/\s+$//g;
        $fieldvalue =~ s/^\s+//g;
    } else {
        $fieldvalue = $line;
    }

    # Skip remaining steps if line was a comment
    next unless (defined($fieldname));

    if (exists($pkg{$fieldname})) {
        $pkg{$fieldname} .= $multiline_seperator . $fieldvalue;
    } else {
        $pkg{$fieldname} = $fieldvalue    
            if ((length($fieldvalue)) and (defined($fieldname)));
    }
}

# For testing only
foreach my $k (sort(keys(%pkg))) {
    print($k, "\t:\t", $pkg{$k}, "\n");
}

__DATA__
a-sendee:
data1
data1
data1
b-sender:
data2
c-date: data3
***************************************
Copyright blah blah blah

d-postage: data4
e-deliverydate: data5

***************************************
unimportant text
f-name: data6

g-paycode: data7
g-paycode: data8

location 1
h-state: data9
i-zip: data10

location 2
h-state: data11
i-zip: data12

[download]
Update: I must admit that I read the question and answered before reading carefully all responses, especially the response by jonjacobmoon, which basically spelled out what I coded.

In reply to Re: Probably very simple (for those in the know) by atcroft
in thread Probably very simple (for those in the know) by Anonymous Monk

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