SMTP client to send search results
SRP - single responsibility principle  

The Send_Email() method is responsible for to many things.
The method is  


creating and configuring a SmtpClient 
creating and configuring a MailMessage
composing the body of the MailMessage 


This should be extracted to separate methods.  

So let us refactor this method.  

First we write a method to create a SmtpClient.

private SmtpClient GetSmtpClient(string serverAddress, int serverPort, bool enableSsl)
{
    SmtpClient smtpClient = new SmtpClient(serverAddress);
    smtpClient.Port = serverPort;
    smtpClient.DeliveryMethod = SmtpDeliveryMethod.Network;
    smtpClient.EnableSsl = enableSsl;

    return smtpClient;
}


This had been pretty easy, hadn't it ? So, next we add a method composing the Subject by using the String.Format() method.

private String ComposeSubject(LogResult logResult) 
{
    return String.Format("Logs from {0} searched {1} for {2}", logResult.ComputerName, logResult.SearchDate, logResult.SearchTerm);
}


But wait, what is LogResult ? That is a class we need to create, so let us do it. As we see it should have at least the properties ComputerName, SearchDate and SearchTerm. We add also a ReadOnlyCollection&lt;String&gt; FileNames property.  

public class LogResult
{
    public String ComputerName { get; private set; }
    public DateTime SearchDate { get; private set; }
    public String SearchTerm { get; private set; }
    public ReadOnlyCollection&lt;String&gt; FileNames { get; private set; }

    public LogResult(String computerName, DateTime searchDate, String searchTerm, List&lt;String&gt; logList)
    {
        ComputerName = computerName;
        SearchDate = searchDate;
        SearchTerm = searchTerm;
        FileNames = ToFileNames(logList);
    }

    public LogResult(DateTime searchDate, String searchTerm, List&lt;String&gt; logList)
        : this(Environment.GetEnvironmentVariable("COMPUTERNAME"), searchDate, searchTerm, logList)
    { }

    private ReadOnlyCollection&lt;String&gt; ToFileNames(List&lt;String&gt; logList)
    {
        IList&lt;String&gt; fileNames = new List&lt;String&gt;(logList.Count);
        foreach (String completeFileName in logList)
        {
            fileNames.Add(Path.GetFileName(completeFileName));
        }
        return new ReadOnlyCollection&lt;String&gt;(fileNames);
    }
}


So now we will use this class to also compose the email body. Here we are using the feature of the StringBuilder that it is returning a StringBuilder for calling the AppendXX() methods. So we can call StringBuilder.Append().Append()...we are using also the StringBuilder.AppendFormat() method. 

private String ComposeMailBody(LogResult logResult)
{
    StringBuilder bodyBuilder = new StringBuilder(1024);

    bodyBuilder.Append("&lt;p style='font-family:arial,helvetica,sans-serif;'&gt;")
        .AppendFormat("Here are the file(s) on &lt;b&gt; {0}", logResult.ComputerName)
        .AppendFormat("&lt;/b&gt; under &lt;b&gt;{0}", logResult.SearchDate)
        .AppendFormat("&lt;/b&gt; that contain &lt;b&gt;&lt;i&gt;{0}&lt;/i&gt;&lt;b&gt;&lt;/p&gt;&lt;br/&gt;&lt;br/&gt;",logResult.SearchTerm)
        .AppendLine("&lt;table width='100%' border='0' align='center' cellpadding='5' cellspacing='0' style='font-family:arial,helvetica,sans-serif;'&gt;&lt;tbody&gt;&lt;tr&gt;&lt;td style='padding:5px;background-color:rgb(169, 169, 169);color:white;'&gt;Filenames&lt;/td&gt;&lt;/tr&gt;");

    int count = 0;
    foreach (String fileName in logResult.FileNames)
    {
        if (count % 2 == 0)
        {
            bodyBuilder.AppendFormat("&lt;tr&gt;&lt;td style='background-color:#bada55;border-collapse:collapse;'&gt;{0}&lt;/td&gt;&lt;/tr&gt;",fileName);
        }
        else
        {
            bodyBuilder.AppendFormat("&lt;tr&gt;&lt;td style='background-color:#55bada;border-collapse:collapse;'&gt;{0}&lt;/td&gt;&lt;/tr&gt;",fileName);
        }
        count++;
    }
    bodyBuilder.Append("&lt;/tr&gt;&lt;/tbody&gt;&lt;/table&gt;");

    return bodyBuilder.ToString();
}


The last method we introduce is for creating a MailMessage.  

private MailMessage CreateMessage(LogResult logResult, String receiver)
{
    MailMessage message = new MailMessage("from-address", receiver);
    message.Subject = ComposeSubkject(logResult);
    message.Body = ComposeMailBody(logResult);

    return message;
}


Now the former Send_Email() method would look like  

private static void SendEmail(string server, int port, bool ssl)
{
    LogResult logResult = new LogResult(sDate ,sSearchTerm, logList);
    SmtpClient smtpClient = GetSmtpClient(server, port, ssl);
    MailMessage message = CreateMailMessage(sEmailAddress);

    smtpClient.Send(message);
}


EmailClass  

Using auto properties will reduce your code a lot. Auto properties are properties with a hidden backing field generated by the compiler.  

public class EmailClass
{
    public string Domain { get; set; }

    public string EmailAddress { get; set; }

    public string FromAddress { get; set; }

    public string Subject { get; set; }

    public List&lt;string&gt; Message { get; set; }

}


Naming  

Based on the naming guidlines method names should be named using PascalCase casing. So Send_Email should be renamed to SendEmail.
Based on the same guidlines method parameters should be named using camelCase casing. the signature of the former Send_Email() method should look like  

private static void SendEmail(string server, int port, bool ssl)