You have to create the content of the body as html.

DECLARE @tabHTML nvarchar(MAX);

SET @tabHTML =

'<table width="90%" border="0" cellspacing="2" cellpadding="2">' +

'<tr>' +

'<td> </td>' +

'<td class="style3">Customer Feedback / Inquiry</td>' +

'<td></td>' +

'</tr>' +

<tr>' +

'<td> </td>' +

'<td><div align="left" style="padding-left:1px"><span class="style2">Reference No.: ' + @RefNo + '</span></div></td>' +

'<td> </td>' +

'</tr>'

....... and so on...

--Get the Recipient

SELECT @Recipient=RouteEmail FROM NatureQuery WHERE NatureCd = @NatureCd;

--Populate the email subject

SET @Subject = 'Ref No. '+ @RefNo + ', ' + @Nature ;

then call the DBMail SP.

EXEC msdb.dbo.sp_send_dbmail @profile_name = 'ContactUs',

@recipients=@Recipient,

@subject=@Subject,

@body = @tabHTML,

@body_format = 'HTML';