I checked the log file and found the message below.
The same user (myself) has other subscriptions that work  and email without a problem.
The report is actually being emailed without formatting.
I can't see what the error below has to do with this problem.

emailextension!WindowsService_0!25a4!04/12/2018-11:37:21:: e ERROR: Error sending email. Exception: System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to write data to the transport connection: An existing connection was forcibly closed by the remote host. ---> System.Net.Sockets.SocketException: An existing connection was forcibly closed by the remote host
 at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size)
 --- End of inner exception stack trace ---
 at System.Net.Sockets.NetworkStream.Write(Byte[] buffer, Int32 offset, Int32 size)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.DelegatedStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.Mime.QuotedPrintableStream.FlushInternal()
 at System.Net.Mime.QuotedPrintableStream.Write(Byte[] buffer, Int32 offset, Int32 count)
 at System.Net.Mime.MimePart.Send(BaseWriter writer)
 at System.Net.Mime.MimeMultiPart.Send(BaseWriter writer)
 at System.Net.Mail.SmtpClient.Send(MailMessage message)