* Received: If you're talking about the act of sending something, the opposite is receiving it.
* Unsent: This directly indicates that something was not sent.
* Returned: If you're talking about a package or email, the opposite could be returned.
* Withdrawn: This could be used in situations where you want to undo the sending of something, like a letter or a message.
For example:
* Sent: "I sent you an email yesterday."
* Received: "I received your email yesterday."
* Unsent: "The letter was unsent due to a technical error."
* Returned: "The package was returned to sender because of an incorrect address."
* Withdrawn: "The politician withdrew his controversial statement after public backlash."
To determine the best opposite of "sent," consider the specific context and the action you want to convey.