Last week I've spent few hours fighting really weird problem. One of our clients host their website at GoDaddy's shared hosting. There is a contact form on this site, that after being filled with some data sends email to site owners. We've been testing this feature on our developments environment and our local production servers and everithing worked just fine. But after we moved to GoDaddy's hosting emails just stoped working. I've spend couple hours trying different approaches using both - new System.Net.Mail (.NET 2.0) and deprecated System.Web.Mail (.NET 1.1) namespaces. Same thing, works at our environment and doesn't work at GoDaddy's hosting.
That's where I gave up and started on googling. I stampted on this post at ASP.NET forum and that's what solved my problem. Turns out GoDaddy doesn't allow to use any smtp servers other than ones they host. Unfortunate thing is that our customer host email server at their ISP and all my attempts to create email account ended up with "pening. validating MX record" status. I found solution by using GoDaddy's smtp relay smtpout.secureserver.net. In order to use it you had to create domain level email acount (for another domain this customer use) through their online "Hosting Account" console and for this account enable smtp relay. Unfortunatelly they limit it to 250 messages per day but that was more than enough in our case. Hope this will help somebody to find a quick way out, out of the shared hosting forest. 