Currently, folding and encoding of e-mail headers is completely left to the user. As commons-email is aimed at simplification of the Java Mail API, the encoding and folding issues should be taken care of by commons-email.
The method buildMimeMessage() in Email.java should be changed as follows:
if (this.headers.size() > 0)
Iterator iterHeaderKeys = this.headers.keySet().iterator();
String name = (String) iterHeaderKeys.next();
String value = (String) headers.get(name);
this.message.addHeader(name, MimeUtility.fold(name.length() + 2, MimeUtility.encodeText(value, this.charset, null)));