Resize Reading Pane Limited

New Outlook for Windows does not currently provide a setting to make the right-side Reading Pane exactly one-third or one-quarter of the window; its responsive layout enforces minimum pane widths.

The divider can be dragged only within those layout constraints. A closely matching New Outlook case confirms that pane widths switch at predefined responsive-layout thresholds rather than allowing unrestricted sizing.^1^

Supported alternatives

Select View → Layout → Reading Pane, then choose the arrangement that works best:

• Show on the bottom — provides more horizontal room for the message list and email.
• Fill screen — selecting a message uses the available window space.
• Popout only — removes the Reading Pane; double-click a message to open it separately.
• Show on the right — retains the current layout, subject to the minimum-width restriction.

These are the documented Reading Pane layouts in New Outlook; there is no documented percentage or fixed-width control.^2^

Changing View → Zoom only changes the size of the email content; it does not change the pane’s physical width.

Request unrestricted resizing

In New Outlook, select:

1. Help
2. Feedback
3. Report an issue
4. Request unrestricted Reading Pane resizing or a configurable width percentage.

Include the desired range—such as 25–33%—and a screenshot with personal information removed. This is the recommended route for this responsive-layout limitation.^1^

If your organization permits Classic Outlook, it may provide a more suitable layout, but switching clients is an administrative or deployment decision rather than a New Outlook setting.

References

1. Single-Line View - NEW Outlook - Microsoft Q&A
2. [New Outlook](https://support.microsoft.com/outlook/use-and-configure-the-reading-pane-to-preview-messages-in-outlook)