Short answer

Use Preview & test in the email editor: Preview as a contact, Preview in an email client, Preview web version, and Send test email. In the test dialog you can pick a contact to send it as. HubSpot's KB says the test arrives from noreply@hubspot.com with the from name Marketing Email Preview Send, so do not judge your From name from a test.

1. The menu

My demo portal's email editor, Preview & test menu open.

Preview and test menu with Preview as a contact, Preview in an email client, Preview web version, Send test email and Copy shareable link — Preview options (1) and Send test email (2).

2. What to check

Personalization tokens and their defaults. See token defaults.
Smart content for different contacts. See smart content.
Links and the footer address. See footer address.

3. Share for review

Copy shareable link lets reviewers see a preview without logging in.

Sources

HubSpot Knowledge Base: Send a test marketing email
HubSpot Knowledge Base: Create and send marketing emails

Send a test marketing email and preview it as a real contact

Short answer

1. The menu

2. What to check

3. Share for review

Sources

New field notes by email

Still stuck?