Adicione isto ao seu arquivo de configuração:
DenyFlags "\Recent"
Como está escrito aqui:
You are strongly advised to use DenyFlags “\Recent”. If the mailbox you are trying to copy has some messages marked by the server “\Recent” this flag can not be carried over (as per RFC). With the denyflag, IMAPcopy will ignore the resent flag. Otherwise, this will result in an error. And the /resent messages will not be copied.