In New Outlook, an email's font size may appear different due to message zoom settings, inherited formatting from the original email, or changes to your default compose settings.
The appropriate solution depends on the cause:
1. Accidental Zooming (Most Common)
You may have accidentally changed the zoom level while reading or composing an email.
2. Inherited Formatting
When replying to or forwarding an email, Outlook may inherit the original sender's font size, style, spacing, or other formatting.
3. Default Compose Settings Have Changed
Your default composing font settings may have been changed.
Additional Tip
If only a single email appears unusually large or small, the issue is often related to the formatting of that specific message rather than your Outlook settings.