The AttachFile method attaches the specified file to the
current message. If the message already contains one or more file
attachments, then it is added to the end of the message. If the
message does not contain any attached files, then it is converted
to a multipart message and the file is appended to the message.
The FileName argument specifies the name of the file to
be attached to the message. If the file is empty or does not exist,
an error will be returned.
The Options argument specifies the type of encoding that
will be applied to the attachment. If this argument is not
specified, then text files will not be encoded and binary files
will be encoded using the standard base64 algorithm.
This method will return value of zero if the action was
successful. Otherwise, a non-zero error code is returned which
indicates the cause of the failure.