bool valid = true;
try
{
    MailAddress address = new MailAddress(email);
}
catch(FormatException)
{
    valid = false;
}

if(!(email.EndsWith("@home.co.uk") ||
     email.EndsWith("@home.com") ||
     email.EndsWith("@homegroup.com")))
{
    valid = false;
}

return valid;

^[A-Z0-9._%+-]+((@home.co.uk)|(@home.com)|(@homegroup.com))$

string emailAddress = "jim@home.com";
string pattern = @"^[A-Z0-9._%+-]+((@home.co.uk)|(@home.com)|(@homegroup.com))$";
if (Regex.IsMatch(emailAddress, pattern, RegexOptions.IgnoreCase))
{
    // email address is valid
}

Dim emailAddress As String = "jim@home.com"
Dim pattern As String = "^[A-Z0-9._%+-]+((@home.co.uk)|(@home.com)|(@homegroup.com))$";
If Regex.IsMatch(emailAddress, pattern, RegexOptions.IgnoreCase) Then
    ' email address is valid
End If

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[x01-x08x0bx0cx0e-x1fx21x23-x5bx5d-x7f]|\[x01-x09x0bx0cx0e-x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[x01-x08x0bx0cx0e-x1fx21-x5ax53-x7f]|\[x01-x09x0bx0cx0e-x7f])+)])

[A-Z0-9._%+-]+@home(.co.uk|(group)?.com)

"[A-Z0-9._%+-]+@home(\.co\.uk|(group)?\.com)"

Regex matcher = new Regex(@"([a-zA-Z0-9_-.]+)@((home.co.uk)|(home.com)|(homegroup.com))");

if(matcher.IsMatch(theEmailAddressToCheck))
{
    //Allow it
}
else
{
    //Don't allow it
}

using System.Text.RegularExpressions;

public static bool ValidEmail(this string email)
    {
        var emailregex = new Regex(@"[A-Za-z0-9._%-]+(@home.co.uk$)|(@home.com$)|(@homegroup.com$)");
        var match = emailregex.Match(email);
        return match.Success;
    }

string emailAddress = "someone@home.co.uk";
if (Regex.IsMatch(emailAddress, @"^[A-Z0-9._%+-]+@home(?:.co.uk|(?:group)?.com)$", RegexOptions.IgnoreCase))
{
    // email address is valid
}

string emailAddress = "someone@home.co.uk";
if (Regex.IsMatch(emailAddress, @"^[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*@home(?:.co.uk|(?:group)?.com)$", RegexOptions.IgnoreCase))
{
    // email address is valid
}