Paul's second letter to the Corinthians dispatched including message without content for fun (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Paul’s second letter to the Corinthians dispatched, including message without content for fun <p> A <ul> (“second” means second letter only) + MU (=letter to the Corinthians, i.e. of the Greek alphabet) + [ M <essag> E (“without content” means all middle letters are dropped) in SENT (=dispatched)]