This was already mentioned before but miral started a thread asking to make it possible to select multiple items and send to retainers bag instantly instead of one by one.

Quote Originally Posted by Triairy View Post
こんばんは。
Good evening,

以前、NPCへの一括売却に関しても同様のコメントをさせていただきました が、現在の通信の仕様上、1度にまとめて情報をサーバーに送ることができません。そのためただ単に実装をしてしまうとマクロのように、1件1件処理が行わ れるようなとても奇妙な仕様になってしまうため現行運営中の対応は行いません。
We have commented on this previously about making it possible to sell multiple items at once to the NPC but due to current systems communication setup we can't sent multiple information to the server at once and for that reason if we do release it, it will work like how macro works where items are processed one at a time. This will be a weird feature so we are not going to implement in current running system.

なお、新生ではまとめて預けるなどには対応する予定ですので、現行運営中はご不便をおかけしますがご了承ください。
We are planning to address this issue in 2.0 to be able to store multiple items at once so we apologize for the inconvenience but if you could please understand, would appreiate.