Email and Mail drop

Email noun - (computer science) a system of world-wide electronic communication in which a computer user can compose a message at one terminal that can be regenerated at the recipient's terminal when the recipient logs in.

Mail drop and email are semantically related. In some cases you can use "Mail drop" instead a noun "Email".

Email and mail drop are semantically related. Sometimes you can use "Email" instead a noun phrase "Mail drop".