MimeMessageWrapper store the whole message content into a byte array if it is constructed from a MimeMessage. This is fast but can raise the memory usage while processing many mails. The copy is only triggered when you have Matchers which not match all or none recipients, but even then its only needed when the message must be altered.
So often the Message is not copied at all. Neverless we should make it configurable to use a temporary file for the copy to save memory. This is best implemented by using a System property