What is Receive Connectors? Provide two default receive connector names?

Receive Connector: By default, when you install the Hub Transport server role, two Receive connectors exist. No additional Receive connectors are needed. The default Receive connectors do not require any additional configuration changes.

Default Receive connector:

(A) Client <Servername>: This Receive connector accepts SMTP connections from all non-MAPI clients, such as POP and IMAP. This connector work on port 587.

(B) Default <Servername>: This Receive connector accepts connections from Edge Transport servers to receive messages from the Internet and from other Hub Transport servers. This connector work on port 25