Hi, this is certainly possible and doable with a Zimlet. The Zimlet API lets you define a REGEX match for text within the Web client to launch an action. For instance, in the following code for an example "com_zimbra_myzimlet.xml" file, the 'matchOn' tag specified the regular expression that you want to match and the onClick tag handle what happens when a match to your regex happens. You can add specialized functionality with your own Java or Javascript code as needed.
Code:
<zimlet name="com_zimbra_myzimlet" version="0.1"
description="My Zimlet" xmlns:html="http://www.w3.org/1999/xhtml">
<include>myzimlet.js</include>
<includeCSS>myzimlet.css</includeCSS>
<handlerObject>Com_Zimbra_Myzimlet</handlerObject>
<contentObject type="myzimlet">
<matchOn>
<regex attrs="ig">([a-zA-Z]{2}[0-9]{4})</regex>
</matchOn>
<toolTip sticky="true" width="250" height="350">
<html:span style="font: 120% Georgia;">Lookup my information externally</html:span>
</toolTip>
<onClick>
<canvas type="window" width="250" height="350"/>
<actionUrl method="get" target="http://my.external.url.com">
<param name="myparameter">${src.$1}</param>
</actionUrl>
</onClick>
</contentObject>
<zimletPanelItem label="My Zimlet" icon="MYZIMLET-panelIcon">
<toolTipText>Click to search my database.</toolTipText>
</zimletPanelItem>
</zimlet>