Autoconfiguration should work; email password can be changed at the webmail interface, or at request be reset by admin@tokerau.org.
“mail.dotplex.com” is the ‘domain name’ of the email sever, behind the colon „:” comes the port number at this server machine. SMTP ~ simple mail transfer protocol, IMAP ~ internet message access protocol, protocol: how computer programs communicate (a definition of the data sent/received), at different ports of the same machine there can run different protocols, server programs or the same protocol with different type of encryption; ssl ~ secure socket layer, tls ~ transport layer security.
… as far as known not available yet
You need a Jabber/XMPP compatible instant messanger, like Conversations for Android (download on tokerau.cc), or Pidgin for Linux and Open-/*-/FreeBSD.
Short name/pseudonym as well as an image/picture of you can usually be configured by your messenger.
A major reason to use XMPP/Jabber rather than Telegram or Signal is that the people/ you who run the server are in possession of the infrastructure. With Telegram the business leader is either punished for not controlling the communication or other·wise users need to fear the entity of the legislator who seeks his own interest, which can stand against environmental protection or social engagement. Even if it is fully allowed or legal what wou wanna do, this may be a problem, when the wrong people learn to know and react upon what you are doing!