Transport encryption protects data as it travels between systems, commonly by encrypting a connection with protocols such as TLS. For email, this may secure the connection between a sender’s mail server and a recipient’s mail server, helping prevent network observers from reading or altering traffic in transit.
It does not necessarily encrypt the message itself end to end. Mail servers may be able to access content after a protected connection terminates, and messages may be sent over unencrypted links if a secure connection cannot be established. Attackers may target those gaps, while defenders configure TLS, monitor delivery settings, and use content encryption when messages must remain protected from intermediary systems.