what are the possible reason for while receiving email alert show me the html tag

Hey Keshav, 

This is a known Rich-Text-Formatted Body mismatch, your Body input is being fed rich text content, but the action isn't set to render it as HTML, so it shows the raw <p> tags instead of formatted text. 

Fix in your Flow's Send Email action: 

1. Find the Body/Text Template resource you're using 

2. If your Text Template resource is set to Rich Text, you must also set Rich-Text-Formatted Body = True on the Send Email action, this tells Salesforce to render the HTML instead of showing it as plain text 

3. If you don't need formatting at all, switch the Text Template to Plain Text instead, mixing Rich Text content with a Plain Text body setting is exactly what produces raw tags like <p>...</p> in the email 

Also, since your screenshot shows Gmail flagging this as spam, that's a separate issue, likely caused by using a Trailhead Playground's default noreply/

sending domain without proper SPF/DKIM setup, not related to the HTML tag issue. 

Reference: