What is reliable? :)

base64 regex

new Regex(@"[0-9a-zA-Z\+/=]{20,}");

'(^Content-Transfer-Encoding: base64$)(^$)(^(([A-Za-z0-9+/=]){4}){1,19
+}$)*(^$)'

^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$


my $sanitized_str = join q{}, grep {!/[^A-Za-z0-9+\/=]/} split /\n/, $
+str;
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