diff --git a/src/net/maildir/maildirFolder.cpp b/src/net/maildir/maildirFolder.cpp
index 4f0acaf3..9a52171c 100644
--- a/src/net/maildir/maildirFolder.cpp
+++ b/src/net/maildir/maildirFolder.cpp
@@ -945,6 +945,8 @@ void maildirFolder::copyMessageImpl(const utility::file::path& tmpDirPath,
 			if (progress)
 				progress->progress(total, size);
 		}
+
+		os->flush();
 	}
 	catch (exception& e)
 	{