SMTP Send is locking up my files - c#

Question

I have a function thats sending messages ( a lot of them) and their attachments.

It basically loops through a directory structure and creates emails from a file structure for example

 c:\emails\message01
                \attachments
 c:\emails\message02
                \attachments

The creation of the messages takes place using .net c#, standard stuff.

After all messages are created... I have another function that runs directly afterwards that copies the message folder to another location.

Problem is - files are locked...

Note: I'm not moving the files, just copying them....

Any suggestions on how to copy locked files, using c#?

Update

I have this add attachments method

    private void AddAttachments(MailMessage mail)
    {
        string attachmentDirectoryPath = "c:\messages\message1";
        DirectoryInfo attachmentDirectory = new DirectoryInfo(attachmentDirectoryPath);
        FileInfo[] attachments = attachmentDirectory.GetFiles();
        foreach (FileInfo attachment in attachments)
        {
            mail.Attachments.Add(new Attachment(attachment.FullName));
        }
    }

Answer 1

How are you reading the files to create the email message? They should be opened as read-only, with a FileShare set to FileShare.ReadWrite... then they shouldn't be locked. If you are using a FileStream you should also wrap your logic in the using keyword so that the resource is disposed properly.

Update:

I believe disposing the mail message itself will close resources within it and unlock the files:

using (var mail = new MailMessage())
{
    AddAttachments(mail);
}
// File copy code should work here