Tigase Administration Guide
Old Way - Editing Configuration File Manually

This is the most likely thing to change after you install server and generate default configuration. Actually it is also the easiest option to customize.

Open tigase-config.xml in you favorite text editor and search for string: "admins". You should find section looking like this:

<entry type="String[]" key="admins">
    <item value="admin%40your.hostname.com"/>
    <item value="admin%40localhost"/>
</entry>

Characters "%40" stand for '@'. So assuming you have just 1 admin account on your installation which is: "frank@jabber.example.com" you need to replace above code with:

<entry type="String[]" key="admins">
    <item value="frank%40jabber.example.com"/>
</entry>

And yes, you can just remove second entry with admin account: "admin@localhost" unless you really want to keep it. Be aware though all system messages will be sent to ALL admin accounts.

Well, if the account does not exists the message is discarded and a warning is be printed in log file. Again, read it again, the previous sentence…​

It means that the admin account has to be also created in normal way on the Jabber server. Just register it using your Jabber client. The admin accounts setting works just as a forward instruction. So as a result all system and admin messages are forwarded to all admin accounts if they exist.

Obviously you can have admin accounts as many as you like:

<entry type="String[]" key="admins">
    <item value="frank%40jabber.example.com"/>
    <item value="lucy%40jabber.example.com"/>
    <item value="mark%40jabber.example.com"/>
    <item value="brenda%40jabber.example.com"/>
    <item value="luck%40jabber.example.com"/>
</entry>