Reading your symptom it sounds like the wrong colour profile is being used. These profiles are mostly associated with the photo paper stocks, so if one of these was incorrectly selected then it could explain the output.
When you select to print from Mail, change the Mail menu in the Print dialog to Color Matching and ensure that 'Canon Color Matching' is selected. Then change the menu to 'Quality & Media' and ensure that Media Type is set to Plain Paper and that Print Quality is set to Standard. Note that with Print Quality set to Fast you will get light-gray text.
With the above settings selected, if you are still getting light output of text and pale colours then there could be something wrong with the Canon driver you are using. Can you confirm that you are using v10.30.3.0 of the driver. This can be determined via Print & Fax. With the printer selected open Options & Supplies and look at the General tab for the driver version.
I just tested a print from Mail to my iP5200R, which is using the v10.30.3.0 driver, and the black text printed correctly. The From, Subject and Date tags did print as gray. Would you say that your gray text is the same level of gray as the Subject tag?
Note that the light gray output could be the result of the black head leaving gaps between the black ink droplets, such as what occurs when Fast Print Quality is selected. Or it could be a result of mixing other colours, like magenta, with the black to achieve the lighter output, which is what occurs with the Mail header tags. If you were to look at the text with a magnifying glass, which of the two causes would be most likely what is occurring for you?