This suggestion comes compliments of mkayuri.

Thanks!
Dave
---------------------------------- Appreciate your great work on this error.
I thought I tried everything on this site, kept changing this and that and this and that...
When I used local smtp relay service, it works fine, but my case sends e-mail to the outside SMTP server (instead of localhost SMTP relay service) with SMTP Authentication;
I solved mine with adding the timeout setting;
MailMessage msg = new MailMessage();
...
msg.Fields.Add("http://schemas.microsoft.com/cdo/configuration/smtpconnectiontimeout", 60);

The default value for smtp connection timeout is 30seconds. I just beefed up that part. I guess, 30 seconds wasn't enough for all SMTP connection (incl. name resolution, user authentication, etc. ).

I've been reading all small prints on this site and contemplating. But, somehow I got this solution so I wanted to say thank you and here's my due. :-)

I hope this might help someone else!