use HTML::Entities;

my $encoded = "Очень Ва&#107
+8;ная Бизнес-&#
+1064;кола";

my $decoded = decode_entities($encoded);
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This gives you a Perl text (unicode) string that you can then encode into whatever output encoding you need, e.g. UTF-8.

Update: for background info on encoding non-ASCII text in email headers (like the Subject: line), see RFC 2047 — though most mail user agents should handle that for you, when configured properly.