If you use Google's Chrome browser with SquirrelMail, you may have noticed that you aren't given the option to compose new messages or replies in HTML (also known as "rich text").  So, you can't do any kind of formatting other than plain text.  The situation happens no matter what your SM option settings are for HTML composition.

That's a known issue in the SM developer community.  A fix is in development (we have tested an early copy of it), but -- since the work is done by volunteer developers with many demands on their personal time -- we can't predict when a stable version of the SM plugin "html_mail" will be available.  We have offered to test future iterations, and we will upgrade it locally when the developer feels it is stable enough to not cause problems.

By the way, technically advanced users can figure out how to configure Chrome to claim it is actually FireFox or Internet Explorer, but that's not good enough for this problem.  The HTML editor is a JavaScript component that runs in the browser, and it doesn't work properly in Chrome due to differences in browser JavaScript implementations.  To use the HTML editor, for now you have to really be using one of those other browsers.