Hello all, I work part time for a company as the IT guy while I'm taking classes...fun stuff I know. Anyway, we have an email problem that has left me stumped. We have two email domains hosted by two different companies...1and1 and Interland. We have about half our employees on one, half on the other, all using Outlook 2003. Our 1and1 employees are having difficulty sending email to our Interland employees. About 50% of the time, the email sent will be refused by Interland and will be sent back saying it could not be delivered. Otherwise, it will go through fine. I've sent email to the Interland accounts from my Gmail, Hotmail, College, and Yahoo accounts, and all 4 go through fine with no bouncebacks. The problem only occurs if we are sending from 1and1, so it's obviously the SMTP server for 1and1 that is causing the problems. What in the world would cause this??? At first I thought Interland had blocked 1and1, but why would some go through and others not? Thanks for any help you guys can give!