Если GET слишком длинный, вы можете использовать POST, вместо этого у вас будет ограничение в 16 КБ, что более чем достаточно. Я использовал код ниже, чтобы сгенерировать ваш график, и это сработало. Так что да, я думаю, вы могли бы использовать этот пост и прикрепить его к электронному письму. Возможно, проблема с использованием GET связана с тем, что почтовый клиент настроен так, что он не открывает файлы изображений, проверяли ли вы его на других клиентах?
<form action='http://chart.apis.google.com/chart' method='POST' id='post_form'>
<input type="hidden" name="cht" value="lc" />
<input type="hidden" name="chtt" value="Demo chart" />
<input type="hidden" name="chg" value="3.85,0" />
<input type='hidden' name='chs' value='900x300' />
<input type="hidden" name="chxt" value="x,y,r,t" />
<input type="hidden" name="chds" value="0,5037" />
<input type="hidden" name="chxl" value="0:|6/22|6/23|6/24|6/25|6/26|6/27|6/28|6/29|6/30|7/1|7/2|7/3|7/4|7/5|7/6|7/7|7/8|7/9|7/10|7/11|7/12|7/13|7/14|7/15|7/16|7/17|7/18|1:|0|503|1006|1509|2012|2515|3018|3521|4024|4527|5037|2:|Days|3:|Amount ($)" />
<input type="hidden" name="chls" value="3,1,0|3,1,0|3,1,0|3,1,0|3,1,0|3,1,0|3,1,0" />
<input type="hidden" name="chm" value="o,990066,0,-1,6.0|o,990066,1,-1,6.0|o,990066,2,-1,6.0|o,990066,3,-1,6.0|o,990066,4,-1,6.0|o,990066,5,-1,6.0|o,990066,6,-1,6.0" />
<input type="hidden" name="chco" value="000000,CD7F32,A62A2A,0000FF,00FF00,FF6EC7,A8A8A8" />
<input type="hidden" name="chdl" value="Type 1|Type 2|Type 3|Type 4|Type 5|Type 6|Type 7" />
<input type='hidden' name='chd' value='t:0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,420.95,0.00,2725.25,0.00,0.00,0.00,0.00,5036.96,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,47.82|0.0000,7.97,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,4.98,1.99,2.24,0.00,0.00,0.00,0.00,0.00,0.00,0.00,1.99,1.99|0.5100,34.04,0.00,0.00,0.00,0.00,0.00,0.00,1.00,0.00,0.00,0.00,0.00,0.00,0.00,36.77,18.01,18.26,0.00,0.00,0.00,0.00,0.00,8.99,0.00,20.06,14.01|0,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,2.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,4.00|3.0000,0.00,0.00,0.00,0.00,0.00,0.00,0.00,46.98,0.00,257.91,113.25,0.00,0.00,0.00,1.00,24.99,29.99,0.00,0.00,0.00,0.00,0.00,0.00,0.00,60.00,123.92|0,0.00,0.00,0.00,0.00,0.00,0.00,0.00,45.00,0.00,0.00,0.00,0.00,0.00,0.00,20.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,84.00|0,55.99,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,0.00,65.99'/>
<input type="submit" />