Those Mojo Logs really help - should have checked earlier!
I had to log into SmarterMail and disable greylisting under the user tab.
Log Message
2010-03-13 13:41:51,901 ERROR mojoPortal.Net.Email - all retries failed sending email to admin@xxxx.com from admin@xxxx.com, message was: Scott
scottxxx@xxx.com
TEST from IGS contact form - should get forwarded to xxxxx@yahoo.com
HTTP_USER_AGENT: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2) Gecko/20100115 Firefox/3.6 (.NET CLR 3.5.30729)
REMOTE_HOST: 68.14.231.134
REMOTE_ADDR: 68.14.231.134
LOCAL_ADDR: 96.31.33.27
System.Net.Mail.SmtpException: Error in processing.
The server response was: Greylisted, please try again in 900 seconds
at System.Net.Mail.RecipientCommand.CheckResponse(SmtpStatusCode statusCode, String response)
at System.Net.Mail.SmtpTransport.SendMail(MailAddress sender, MailAddressCollection recipients, String deliveryNotify, SmtpFailedRecipientException& exception)
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at mojoPortal.Net.Email.Send(SmtpSettings smtpSettings, String from, String replyTo, String to, String cc, String bcc, String subject, String messageBody, Boolean html, String priority, String[] attachmentPaths, String[] attachmentNames) in C:\TempProjects\Mojo_IGS\mojoPortal.Net\Email.cs:line 725
2010-03-13 13:42:00,231 INFO mojoPortal.Web.WebTaskManager - started WebTaskManager task