email font very small only when composing messages

You can change the setting for Zoom While Composing. If the e-mail you are composing is open in a separate window, go to the Format Text tab and click Zoom. Choose the desired zoom ratio in the Zoom While Composing dialog box.

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:

1. Reset zoom while composing
2. Open a new email.
3. Place the cursor in the message body.
4. Press Alt+H, then F, then S to move focus to the font size box.
5. Type a normal size (for example 11 or 12) and press Enter.
6. If the text still looks tiny, use the Zoom control on the status bar (bottom-right) and set it to 100%.
7. Check/change the default compose font size
8. Select File > Options > Mail > Stationery and Fonts.
9. Under New mail messages, select Font.
10. Choose a normal Size (for example 11 or 12) and click OK.
11. Under Replying or forwarding messages, do the same if replies/forwards are also tiny.
12. 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:

• Create, change, or customize a view in Outlook
• Use a screen reader to format text in your email in Outlook