I think that your strings are Quoted Printable. Try to use MIME::QuotedPrint module:

use MIME::QuotedPrint;

my $msg = <your string>;
$msg =~ s/=\?ISO-8859-1\?Q\?//g; # Cut a charset information and a cri
+terion of quoted print string.
$msg =~ s/\?=//g; # Cut a criterion of quoted print string end. 
$msg = MIME::QuotedPrint::decode($msg); # Decode string
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SV* sv_bless(SV* sv, HV* stash);