Envelope of Sending (5e Equipment)
From D&D Wiki
Wondrous item, common
When a sheet of paper or tiny item is placed in this envelope, the user can specify a recipient as long as the recipient's name (or a name the sender associates with the recipient) is written on it. If the recipient is within 5 miles, the letter flies toward them and arrives within 10 minutes. If not, the letter is not sent. If the recipient moves out of range or transports itself to another plane of existence as the letter is being sent, the letter arrives at the recipients location as of sending.