You can. Here’s what you do:

1. Click Options in the upper-right corner of your Mail page.
2. From the list on the left side, click General.
3. Find “When I first visit Mail.” Check “Show me the Inbox.”
4. Above the options area, click Save Changes.

Done! Anytime you’d like to turn the Welcome page back on, un-check the “Show me the welcome page” box.