Initializes a struct listserv* and makes possible subsequent execution of commands over TCPGUI.
If password is NULL, the parameters are read from a config file. For defails, see configuration-file.
If no configuration file is found, an error message is printed at stderr, and the function returns NULL.
If email is NULL, then @ is used as email.
The host is in the host:port format. If the :port part is missing, 2306 is assumed.
If host is NULL, localhost is assumed.
listserv_init does not check if it is possible to connect with the provided information, the email/password/port combination is valid, or if listserv is runniung.