I cannot send mail using Outlook 2007 under Vista Enterprise; it used to work but without any obvious changes to the settings it stopped functioning.

I'm very sorry to hear that. To receive some useful help you will need to provide more detail (i.e. are you using Exchange, POP3, any error messages, was it working with an older version of Outlook, is this an upgrade or a clean install, is your internet connection working, were there any non-obvious changes recently made, etc.). The better you describe your situation, the more likely you will get your problem solved. Unless, of course, you were merely venting...
Tim
"p1024"

This is the message I get when I try to send email:
Het verbinding maken met de server is mislukt. Onderwerp '', Account: 'pop.zonnet.nl', Server: 'smtp.zonnet.nl', Protocol: SMTP, Poort: 25, Beveiligd(SSL): Nee, Socket-fout: 10060, Foutnummer: 0x800CCC0E
I have Outlook 2007 running under Vista Enterprise. No defender, firewall or antiviral software running. I have checked all the settings : SMTP etc. contacted my ISP and all seesm to be the way it should be.
"Tim" wrote:

Actually I get another mesage as well:
'Peter Hoeben' op 08/05/2007 17:49 553 sorry, relaying denied from your location [62.166.11.184] (#5.7.1)
Anybody that can help? Thanks.
"p1024" wrote:

p1024 wrote:

Het verbinding maken met de server is mislukt. Onderwerp '', Account:

This error message indicates that you are on Versatel.net. You are trying to send mail through another ISP (relaying) and Versatel doesn't allow that. The Whois lookup indicates that Versatel is owned (or called) "Zon Internet" but you may have an incorrect smtp server listed. Since I don't know anything about Dutch ISP's, that's just a guess.
So perhaps this is a laptop that works well when you are connected to the "Zon Internet" ISP at home but not at the office when you are connected via Versatel? Since you didn't give much detail about your machine or what changed between the time things worked and the time they didn't, that's my best guess.
Malke Elephant Boy Computers elephantboycomputers.com "Don't Panic!" MS-MVP Windows - Shell/User

I agree, it's caused by the ISP hosting your email account. On my account, I had to do the following, in Outlook:
Go to Tools / Account Settings Select the account, click Change Click the More Settings button Click the Outgoing Server tab Check the box that says My outgoing server requires authentication
Of course, if yours are in Dutch, you'll have to translate. I have this box checked and can send email from anywhere, including every foreign country I've been to...(sadly not yours, yet...)
Dana Cline - MCE MVP
"Malke"