Pop3_get is used to retrieve and delete messages from a server
    running the Post Office Protocol version 3 as defined in rfc1725. In its default form it
    returns a vector of vectors containing messages retrieved from the POP3 server.
    Each vector within the vector contains a pair of VARCHAR UIDL and
    VARCHAR Message body, i.e. to get the message body of the second message retrieved,
    one would use aref (aref (msg_vec, 1), 1).
    Total length of messages retrieved will not exceed the value of buffer_size
    parameter in bytes.The optional parameter command can be used to control output
    or delete messages. When command
    is passed a VARCHAR @uidl@, pop3_get outputs single
    vector containing VARCHAR UIDLs. The buffer_size constraint
    is effective here. Thus, the vector will only contain UIDLs of messages whose total message text
    length does not exceed buffer_size bytes. These message lengths are
    cumulated in the order returned by the POP3 server.Command @delete@ will cause retrieved messages to be deleted from the server
    after retrieval.