Contact Form with user id instead of email address?

Hello again,

I’m trying to build a contact form and instead of entering email address, i want the user to enter its user id and I will include the @domain.com on actionscript on the form and on its php.

Something like this:
User id:[COLOR=blue]"________"[/COLOR] ([COLOR=blue]enter by user[/COLOR]) [COLOR=black]@ domain.com (@domain.com will be already on the form)[/COLOR]

so all the user has to do is enter its user id.
this user id will pick up the rest which will be the @domain.com and that would be an email send.

Has anyone done that before?.. any help please!

ActionScript Code:
[FONT=Courier New][LEFT]</p>
<p>on COLOR=#000000[/COLOR] [COLOR=#000000]{[/COLOR]</p>
<p> </p>
<p> [COLOR=#0000ff]if[/COLOR] [COLOR=#000000]([/COLOR]!Email.[COLOR=#0000ff]length[/COLOR] || Email.[COLOR=#0000ff]indexOf[/COLOR]COLOR=#000000[/COLOR] == -[COLOR=#000080]1[/COLOR] || Email.[COLOR=#0000ff]indexOf[/COLOR]COLOR=#000000[/COLOR] == -[COLOR=#000080]1[/COLOR][COLOR=#000000])[/COLOR] [COLOR=#000000]{[/COLOR]</p>
<p> EmailStatus = [COLOR=#ff0000]“Please enter a valid COMPANY E-mail address”[/COLOR];</p>
<p> [COLOR=#000000]}[/COLOR] </p>
<p> [COLOR=#0000ff]else[/COLOR] [COLOR=#0000ff]if[/COLOR] COLOR=#000000[/COLOR] [COLOR=#000000]{[/COLOR]</p>
<p> EmailStatus = [COLOR=#ff0000]“Please enter your message”[/COLOR];</p>
<p> [COLOR=#000000]}[/COLOR] </p>
<p> </p>
<p> [COLOR=#0000ff]else[/COLOR] [COLOR=#000000]{[/COLOR]</p>
<p> [COLOR=#0000ff]loadVariablesNum[/COLOR] [COLOR=#000000]([/COLOR][COLOR=#ff0000]“MailPHP.php”[/COLOR], [COLOR=#ff0000]“0”[/COLOR], [COLOR=#ff0000]“Post”[/COLOR][COLOR=#000000])[/COLOR];</p>
<p> [COLOR=#0000ff]gotoAndPlay[/COLOR]COLOR=#000000[/COLOR];</p>
<p> [COLOR=#000000]}[/COLOR]</p>
<p>[COLOR=#000000]}[/COLOR]</p>
<p>
[/LEFT]
[/FONT]

and this is what i have on my php file


<?
$ToEmail = "email@domain.com";
$ToSubject = "Training Orientation Feedback";
$EmailBody = "Sent By: $FirstName
Senders Email: $Email

Message Sent:
$ToComments
";
mail($ToName." <".$ToEmail.">",$ToSubject, $EmailBody, "From: ".$FirstName." <".$Email.">");
?>

the input text for the user id or email in this case is variable = Email

please help!

thanks.