I regularly get the 550 must be authenticated error when I try to send email. It works fine 8 times out of 10 but then I get the 550 error the other times. If I get it twice with the same email, if I immediately open up Outlook Express and do the same email to the same person, it has always sent OK. so I presume the problem is with Outlook. I am using Outlook 2003 and have applied all the updates and patches. I am using OneandOne as my email servicer provider and am using a 3G internet connection through T Mobile as I live on a boat. Any ideas greatly appreciated. David

I don't know why it works some times and not others. That error normally means that you are trying to use an email server other than that of the ISP you connect to and they have relaying disabled. You might try contacting your ISP for help.

OK Thank you. I will try that