If they use iOS devices, try to have a user navigate to the following links from iPhone, MAC book, or iPad Safar browser?
For 2.abc.com users:
ciscojabber://provision?ServicesDomain=2.abc.com
For 3.abc.com users:
ciscojabber://provision?ServicesDomain=3.abc.com
When they paste this URL in Safari, it will cross launch the Jabber application and automatically use the domain that you inserted in the URL for autodiscovery.
Or, if you want to change the URL into a clickable/tap-able link, you can insert it into the below html script, save it notepad (as html), and email it to the user. This example is for 2.abc.com but you can use the same example to create one for 3.abc.com.
<!DOCTYPE html>
<html>
<head>
<title>Jabber Configuration</title>
</head>
<body>
<p>Click on the Link below. Once Jabber is launched, enter your username and password to sign in.</p>
<a href="ciscojabber://provision?servicesdomain=2.abc.com" target="_self">Click here to launch Jabber</a>
</body>
</html>
To get all three clusters to work under the abc.com, you need to have ILS enabled across all three clusters. Then you can add your expressway e servers (from all three clusters) under the external abc.com public DNS SRV Records, and all your relevant CUCM nodes (from all three clusters) under your internal abc.com internal DNS SRV records.
