As far as I see you mean deobfuscation. Obfuscated variants are
(almost) infinite hence you cannot compute in one easy step what is
and what's not valid e-mail address.

# one poor decision
$_ = 'mike miky [mike [-( at )-] mike.bla]';
/(\w+) \W+ at \W+ (\w+(?:\.\w+)+)/i;
print "$1\@$2" 
# prints mike@mike.bla
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