diff --git a/src/frontend/src/features/layouts/components/mailbox-panel/_index.scss b/src/frontend/src/features/layouts/components/mailbox-panel/_index.scss
index b440f1c8..64e29154 100644
--- a/src/frontend/src/features/layouts/components/mailbox-panel/_index.scss
+++ b/src/frontend/src/features/layouts/components/mailbox-panel/_index.scss
@@ -3,23 +3,25 @@
     flex-direction: column;
     height: 100%;
     max-height: 100%;
-    overflow: auto;
     font-size: var(--c--globals--font--sizes--sm);
     position: relative;
 }
 
 .mailbox-panel__header {
-    position: sticky;
-    top: 0;
-    z-index: 10;
     flex-shrink: 0;
     background: var(--c--contextuals--background--surface--secondary);
+    z-index: 10;
+}
+
+.mailbox-panel__body {
+    flex: 1;
+    min-height: 0;
 }
 
 .mailbox-panel__mailbox-title {
     margin: 0;
     flex-shrink: 0;
-    padding-block: var(--c--globals--spacings--sm);
+    padding-bottom: var(--c--globals--spacings--xs);
 
     & > .c__dropdown-menu-trigger {
         justify-content: flex-start;
@@ -51,13 +53,3 @@
         }
     }
 }
-
-.mailbox-panel .mailbox-list {
-    flex-shrink: 0;
-    margin-bottom: var(--c--globals--spacings--sm);
-}
-
-.mailbox-panel .mailbox-labels {
-    border-top: 1px solid var(--c--contextuals--border--surface--primary);
-    flex: 1;
-}
diff --git a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-actions/_index.scss b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-actions/_index.scss
index 4c3eabf5..f90e140b 100644
--- a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-actions/_index.scss
+++ b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-actions/_index.scss
@@ -1,8 +1,3 @@
-@keyframes mailbox-panel-actions__spin {
-    from { transform: rotate(0deg); }
-    to { transform: rotate(360deg); }
-}
-
 .mailbox-panel-actions {
     display: flex;
     justify-content: space-between;
@@ -15,8 +10,16 @@
         align-items: center;
         justify-content: center;
 
+        @keyframes refreshIconSpin {
+            0% { transform: rotate(0deg); filter: blur(0px); }
+            33% { filter: blur(1px); }
+            50% { filter: blur(2px); }
+            66% { filter: blur(1px); }
+            100% { transform: rotate(360deg); filter: blur(0px); }
+        }
+
         &--spinning {
-            animation: mailbox-panel-actions__spin 700ms ease-in-out infinite;
+            animation: refreshIconSpin 700ms var(--c--globals--transitions--ease-in-out) infinite;
         }
     }
 
diff --git a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-labels/_index.scss b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-labels/_index.scss
index 0a4837d8..0034a1f6 100644
--- a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-labels/_index.scss
+++ b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-labels/_index.scss
@@ -3,7 +3,6 @@
     flex-direction: column;
     height: 100%;
     overflow-y: auto;
-    min-height: 200px;
 }
 
 .mailbox-labels__drag-over-indicator {
diff --git a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-list/_index.scss b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-list/_index.scss
index dedf56f5..83daaf1a 100644
--- a/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-list/_index.scss
+++ b/src/frontend/src/features/layouts/components/mailbox-panel/components/mailbox-list/_index.scss
@@ -3,7 +3,8 @@
     flex-direction: column;
     margin-inline: var(--c--globals--spacings--sm);
     gap: var(--c--globals--spacings--4xs);
-    flex-shrink: 0;
+    height: 100%;
+    overflow-y: auto;
 }
 
 // Wraps a folder link together with its disclosure chevron button. The
diff --git a/src/frontend/src/features/layouts/components/mailbox-panel/index.tsx b/src/frontend/src/features/layouts/components/mailbox-panel/index.tsx
index 994bf160..0c86f245 100644
--- a/src/frontend/src/features/layouts/components/mailbox-panel/index.tsx
+++ b/src/frontend/src/features/layouts/components/mailbox-panel/index.tsx
@@ -8,6 +8,7 @@ import { useSearchParams } from "next/navigation";
 import { useLayoutContext } from "@/features/layouts/components/layout-context";
 import { MailboxLabels } from "./components/mailbox-labels";
 import { useState } from "react";
+import { Group, Panel, Separator, useDefaultLayout } from "react-resizable-panels";
 
 export const MailboxPanel = () => {
     const router = useRouter();
@@ -15,6 +16,10 @@ export const MailboxPanel = () => {
     const { selectedMailbox, mailboxes, queryStates } = useMailboxContext();
     const { closeLeftPanel } = useLayoutContext();
     const [isOpen, setIsOpen] = useState(false);
+    const { defaultLayout, onLayoutChange } = useDefaultLayout({
+        groupId: "mailbox-panel-sections",
+        storage: typeof window !== "undefined" ? localStorage : undefined,
+    });
 
     const getMailboxOptions = () => {
         if (!mailboxes) return [];
@@ -64,11 +69,20 @@ export const MailboxPanel = () => {
             </div>
             {!selectedMailbox || queryStates.mailboxes.isLoading ? <Spinner /> :
                 (
-                    <>
-
-                        <MailboxList />
-                        <MailboxLabels mailbox={selectedMailbox} />
-                    </>
+                    <Group
+                        orientation="vertical"
+                        className="mailbox-panel__body"
+                        defaultLayout={defaultLayout}
+                        onLayoutChange={onLayoutChange}
+                    >
+                        <Panel id="mailbox-panel-folders" defaultSize="40%" minSize="20%">
+                            <MailboxList />
+                        </Panel>
+                        <Separator className="panel__resize-handle" />
+                        <Panel id="mailbox-panel-labels" defaultSize="60%" minSize="20%">
+                            <MailboxLabels mailbox={selectedMailbox} />
+                        </Panel>
+                    </Group>
                 )}
         </div>
     )
diff --git a/src/frontend/src/features/layouts/components/thread-panel/components/thread-panel-filter.tsx b/src/frontend/src/features/layouts/components/thread-panel/components/thread-panel-filter.tsx
index d5026a89..601e44cf 100644
--- a/src/frontend/src/features/layouts/components/thread-panel/components/thread-panel-filter.tsx
+++ b/src/frontend/src/features/layouts/components/thread-panel/components/thread-panel-filter.tsx
@@ -98,7 +98,11 @@ export const ThreadPanelFilter = () => {
         callback: () => handleSelectFilter(type),
       }))}
     >
-      <Tooltip content={getTooltipContent()} className={isDisabled ? "hidden" : ""}>
+    <Tooltip
+        placement="right"
+        content={getTooltipContent()}
+        className={isDisabled ? "hidden" : ""}
+      >
         <Button
           onClick={handleToggleClick}
           disabled={isDisabled}
diff --git a/src/frontend/src/features/ui/components/transient-tooltip/_index.scss b/src/frontend/src/features/ui/components/transient-tooltip/_index.scss
index c3835244..cf69800e 100644
--- a/src/frontend/src/features/ui/components/transient-tooltip/_index.scss
+++ b/src/frontend/src/features/ui/components/transient-tooltip/_index.scss
@@ -6,14 +6,19 @@
 // so we can place it at viewport coordinates from JS, mark non-interactive,
 // and centre horizontally on the trigger's mid-axis.
 .transient-tooltip {
+    --offset: 8px;
     position: fixed;
     z-index: 1000;
     pointer-events: none;
-    transform: translateX(-50%);
+    transform: translate(-50%, calc(-1 * var(--offset)));
 
     &--top {
-        // For top placement, the inline `top` is the trigger's top edge, so
-        // we lift the bubble by its own height to sit above the trigger.
-        transform: translate(-50%, -100%);
+        transform: translate(-50%, calc(-100% + var(--offset)));
+    }
+    &--left {
+        transform: translate(calc(-100% + var(--offset)), -50%);
+    }
+    &--right {
+        transform: translate(calc(-1 * var(--offset)), -50%);
     }
 }
diff --git a/src/frontend/src/features/ui/components/transient-tooltip/index.tsx b/src/frontend/src/features/ui/components/transient-tooltip/index.tsx
index 1db7f378..1a9f948c 100644
--- a/src/frontend/src/features/ui/components/transient-tooltip/index.tsx
+++ b/src/frontend/src/features/ui/components/transient-tooltip/index.tsx
@@ -3,7 +3,7 @@ import { Portal } from "@/features/ui/components/portal";
 
 const DEFAULT_DURATION_MS = 2000;
 
-export type TransientTooltipPlacement = "top" | "bottom";
+export type TransientTooltipPlacement = "top" | "bottom" | "left" | "right";
 
 export type TransientTooltipProps = {
     message: string | null;
@@ -31,6 +31,12 @@ export const TransientTooltip = ({
     const [position, setPosition] = useState<Position | null>(null);
     const [internalMessage, setInternalMessage] = useState<string | null>(null);
     const [isExiting, setIsExiting] = useState(false);
+    // Latest-ref so the auto-hide timer below doesn't reset on every parent
+    // re-render when `onHide` is passed as an inline arrow function.
+    const onHideRef = useRef(onHide);
+    useEffect(() => {
+        onHideRef.current = onHide;
+    });
 
     // Delayed-unmount pattern: when the parent clears `message`, we keep the
     // bubble mounted under `c__tooltip--exiting` so its exit animation can
@@ -54,10 +60,16 @@ export const TransientTooltip = ({
         const updatePosition = () => {
             const rect = wrapperRef.current?.getBoundingClientRect();
             if (!rect) return;
-            setPosition({
-                top: placement === "bottom" ? rect.bottom : rect.top,
-                left: rect.left + rect.width / 2,
-            });
+
+            let top: number, left: number;
+            if (["left", "right"].includes(placement)) {
+                top = rect.top + rect.height / 2;
+                left = placement === "left" ? rect.left : rect.right;
+            } else {
+                top = placement === "bottom" ? rect.bottom : rect.top;
+                left = rect.left + rect.width / 2;
+            }
+            setPosition({ top, left });
         };
         updatePosition();
         window.addEventListener("resize", updatePosition);
@@ -66,9 +78,9 @@ export const TransientTooltip = ({
 
     useEffect(() => {
         if (!message) return;
-        const timer = window.setTimeout(onHide, duration);
+        const timer = window.setTimeout(() => onHideRef.current(), duration);
         return () => window.clearTimeout(timer);
-    }, [message, duration, onHide]);
+    }, [message, duration]);
 
     return (
         <span ref={wrapperRef} className="transient-tooltip__wrapper">
diff --git a/src/frontend/src/styles/globals.scss b/src/frontend/src/styles/globals.scss
index df61b90d..a1b27efb 100644
--- a/src/frontend/src/styles/globals.scss
+++ b/src/frontend/src/styles/globals.scss
@@ -32,18 +32,16 @@ body {
 }
 
 // Customize resize handle to add an hover effect to explicit that
-// this component is interactive.
+// this component is interactive. Orientation is driven by the
+// `aria-orientation` attribute set by react-resizable-panels:
+// "vertical" → vertical line (horizontal Group, drag left/right)
+// "horizontal" → horizontal line (vertical Group, drag up/down)
 .panel__resize-handle {
-  width: 1px;
   background-color: var(--c--contextuals--border--surface--primary);
   position: relative;
 
   &:before {
     content: '';
-    width: 3px;
-    left: -1px;
-    top: 0;
-    bottom: 0;
     background: var(--c--contextuals--border--surface--primary);
     position: absolute;
     opacity: 0;
@@ -51,19 +49,51 @@ body {
     z-index: 10;
   }
 
-  // Little tricks to expand the area to catch hover
+  // Expand the hover catch zone.
   &:after {
     content: '';
-    width: 11px;
-    left: -5px;
-    top:0;
-    bottom: 0;
     position: absolute;
   }
 
   &:hover:before {
     opacity: 1;
   }
+
+  &[aria-orientation="vertical"] {
+    width: 1px;
+
+    &:before {
+      width: 3px;
+      left: -1px;
+      top: 0;
+      bottom: 0;
+    }
+
+    &:after {
+      width: 11px;
+      left: -5px;
+      top: 0;
+      bottom: 0;
+    }
+  }
+
+  &[aria-orientation="horizontal"] {
+    height: 1px;
+
+    &:before {
+      height: 3px;
+      top: -1px;
+      left: 0;
+      right: 0;
+    }
+
+    &:after {
+      height: 11px;
+      top: -5px;
+      left: 0;
+      right: 0;
+    }
+  }
 }