What does the message "This conversation is read-only" mean in my Sell emails?

Question

What does the message This conversation is read-only mean in my Sell emails? Can I delete the email? 

Answer

The email came into Sell from another user's email integration and the original user was not included as the sender or recipient. 

To delete these emails have a Sell admin add the contact or individual email to the blocklist. For complete steps, see the article: Blocklisting leads and contacts to prevent tracking of email conversations.