In classic Outlook for Windows, tiny text while composing is usually caused by either the message zoom level or the default compose font size.
Try these steps in order:
- Reset zoom while composing
- Open a new email.
- Place the cursor in the message body.
- Press
Alt+H, then F, then S to move focus to the font size box.
- Type a normal size (for example
11 or 12) and press Enter.
- If the text still looks tiny, use the Zoom control on the status bar (bottom-right) and set it to 100%.
- Check/change the default compose font size
- Select File > Options > Mail > Stationery and Fonts.
- Under New mail messages, select Font.
- Choose a normal Size (for example 11 or 12) and click OK.
- Under Replying or forwarding messages, do the same if replies/forwards are also tiny.
- Click OK twice to save.
This will affect both the body text and the signature, since the signature inherits the compose font/zoom settings.
References: