diff --git a/melib/src/backends.rs b/melib/src/backends.rs
index 0365db09e..e6e50ba63 100644
--- a/melib/src/backends.rs
+++ b/melib/src/backends.rs
@@ -437,6 +437,9 @@ pub trait MailBackend: ::std::fmt::Debug + Send + Sync {
 /// ```
 pub trait BackendOp: ::std::fmt::Debug + ::std::marker::Send {
     fn as_bytes(&mut self) -> ResultFuture<Vec<u8>>;
+    fn copy_to(&self, _mailbox_hash: MailboxHash) -> ResultFuture<()> {
+        Err(MeliError::new("Unimplemented."))
+    }
     fn fetch_flags(&self) -> ResultFuture<Flag>;
     fn set_flag(&mut self, flag: Flag, value: bool) -> ResultFuture<()>;
     fn set_tag(&mut self, tag: String, value: bool) -> ResultFuture<()>;