It is a shame that Microsoft did not include this feature to allow users to default the font size of email messages for reading. It makes it hard for some users who have bad eye sight.
To set a default text size for the email messages, I will recommend you changing the standard mail text to plain text.
1. Open Microsoft Outlook and click on File
2. Options, Trust Center and Trust Center Settings
3. Email Security and Tick "Read all standard mail in plain text" and "Read all digitally signed mail in plain text.
4. OK to apply the settings.
5. Go back to File, Options, Mail and select Stationery and Fonts
6. Go to individual tab settings to change the font size.
- Change new mail messages,
- Replying or forwarding messages
- Composing and reading plain text messages
7. Close Outlook and reopen, huala!