[Plugin: Contact Form 7] Mail not sending in contact form 7

Hai,
I am using contact form 7 to create contact us page .In my form only email and name are mandatory fields.but if i click submit button after providing only email and name, success message is not coming.the success message is displaying only if i select checkbox ‘requirement’ along with providing email and name.
do u know why it is happening.

here is the code i use

<table id = "contactform">
<tr>
<td class = "contacttext">Requirements:</td>
<td class = "radiotext">[checkbox requirements "Retail" "Office" "Other"]</td>
</tr>
<tr>
<td class = "contacttext">* Email:</td>
<td>[email* youremail 25/ class:contacttextinput]</td>
</tr>
<tr>
<td class = "contacttext">* Name:</td>
<td>[text* yourname 25/ class:contacttextinput]</td>
</tr>
<tr>
<td class = "contacttext">Location (area or grid):</td>
<td>[text location 25/ class:contacttextinput ]</td>
</tr>
<tr>
<td  class = "contacttext">Comments:</td>
<td width = "200px">[textarea comments 30x5 class:contacttextinput]</td>
</tr>
</table>
<div  align = "center">
[submit "submit"]<input type="reset" value="Clear">
</div>

Mail
From: [yourname] <[youremail]

Name:[yourname]
The requirement is:[requirement]
Location (area or grid):[location]
Comments:[comments]

http://wordpress.org/extend/plugins/contact-form-7/