The code worked after I added these four lines before the send.
myMail.Configuration.Fields.Item ("schemas.microsoft.com/cdo/configuration/sendusing") = 2
myMail.Configuration.Fields.Item ("schemas.microsoft.com/cdo/configuration/smtpserver") = "localhost"
myMail.Configuration.Fields.Item ("schemas.microsoft.com/cdo/configuration/smtpserverport") = 25
myMail.Configuration.Fields.Update