Please be advised that sending 2007 versions of PowerPoint (.pptx) through email and retrieving them through Webmail is not the best method for getting files to classroom computers. The webmail program does not process the extra data associated with this file type well. Webmail wants you to save the file as a zip or compressed file making it very difficult to display properly in Powerpoint.
If you want to use Webmail to retrieve Powerpoint files on classroom computers, your best option is to save the file as a 97-2003 version (.ppt).
When saving a PowerPoint created in 2007 as an older version you may get a warning about some slides losing some compatibility features. Please do not worry about this, that warning only means that those slides would be un-editable if they were opened by an older version of the program. You will still be able to edit them and they will still display correctly.
A reminder that if you are emailing for retrieval in a classroom, we strongly suggest using network drives instead to avoid these issues all together.