How to increase the VIEW size when composing messages in Apple Mail

LCIE25 wrote:

When I am composing messages in Apple Outlook

Outlook is not from Apple, it's from Microsoft. If you are really using that, then you should go to the MS forums instead of here for help.

If you are in fact using Apple Mail, then set the size you want in Mail > Preferences > Fonts and Colors > Message Font. You can make it as large as you want, it does not affect what is seen at the other end. That is determined by the settings on the recipient computer (unless you make special settings yourself in the New Message pane for every outgoing individually).

These are two icons Apple has used for their application called "Mail"

Whereas this is what Microsoft Outlook typically looks like

Please clarify which program you are using?

Any email beyond plain ASCII text is going to be inconsistent at best across email clients, or within the same email client. Mail has Mail menu -> Preferences for composition. If you want your mail to be consistent, use plain text. Use symbols like *for bold*. The lower case o for bullets, and underscore to indicate multiple spaces. Sadly no one has made a consistent email format.