Don't quite understand which bits of your code are where (nor do I see what you're trying to achieve with all those @ signs and eval() calls), but it looks like you're trying to build $internal_message_email_send before you've got the values of the variables you're trying to build it with.
Okay, now I think I see what you're trying to achieve here. $internal_message_email_send = "blah" is supposed to be a kind of template. Don't know why you thought @ would help, but hey....
$internal_message_email_send =
'"Dear Mr/Ms : ".$fullnamecontent."<br><br> We created your account at ".$domainnamecontent."<br>
as ".$classificationstatus." with a membership type ".$membershipstatus." <br> You may login anytime by visiting the site
<br><br>
Current Status : ".$currentstatus."<br><br>
Thank you very much !! "';
and
eval('$body='.$internal_message_email_send.';');
Something along those lines anyway. I may have a ' or " too few or too many somewhere.
Usually though if eval() is the answer then the question probably needs rethinking.