What does Email Server mean?
A mail server is an application or computer that acts as a virtual postal office. The server stores the incoming mail and distributes it to local users. It also sends out outgoing messages. This model uses a client/server application to send and receive messages via Simple Mail Transfer Protocol (SMTP).
A mail server can also be called a message or message transfer agent.
Techopedia explains Email Server
An email server is a computer that has mail transfer agent (MTA), functions. Mail is exchanged between special software-based email servers that use standard protocols to handle messages and multimedia content.
An email server receives mail sent from an MTA, an MUA (mail user agent), or an MSA (mail submission agent). SMTP defines the details of each transmission. If an MTA receives mail from a recipient that is not located locally, the mail will be forwarded to another MTA. The MTA places a “received trace header” on the message’s top header every time this happens. This displays all MTAs who handled the message prior to it reaching the recipient’s mailbox. Administrators can see if the optimal route was followed.