Civimail produces saving error when sending test
I went in and submitted a test mailing that I wasn't able to preview. This caused the cronjob to spit out the error: 

&lt;br /&gt;
&lt;b&gt;Fatal error&lt;/b&gt;:  Call to undefined function mb_strtoupper() in &lt;b&gt;/home/ourbase/public_html/sites/all/modules/civicrm/packages/html2text/rcube_html2text.php&lt;/b&gt; on line &lt;b&gt;703&lt;/b&gt;&lt;br /&gt;


The key there is the function mb_strtoupper() [that's "string to upper"]. To fix this, you need to enable "mbstring" on your php/apache build. In my case, this was done through the WHM interface as follows: 


Go to EasyApache
Customize the current profile
On Step 3 (?) click on "Exhaustive Options"
Check the checkbox for MBString
Build &amp; Compile (takes a while), and wait until it's done.


If you don't have access to that solution, consider one of these lesser temporary solutions while you wait for someone to resolve it:
1. Remove all &lt;strong&gt; and/or &lt;b&gt; tags or...
2. Manually put text in the plain text box