Hi, There are mails I can not send. I get back a "Diagnostic-Code: smtp;450 4.7.1 <unknown[194.78.127.146]>: Client host rejected: cannot find your hostname" On other mails I get this back: "<hb1819 #5.7.1 smtp;554 5.7.1 Invalid HELO... REJECTING!> " Things I've done: Exchange System Manager - Administrative Groups - <server> - Protocols - SMTP - Default SMTP Virtual server -properties - delivery - advanced - check the FQDN (is correct) Exchange System Manager - Administrative Groups - <server> - Routing Groups - First Routing Group - Connectors - SMTP Internet Connector - properties - advanced - send helo instead of ehlo (check and uncheck) DNS checked on A-record and PTR-record Telnet is not possible because ISP blocked port 25 SMTPdiag from Microsoft cannot launch (nothing happens) Don't find any log-file Using a windows server 2003 SP2

Two questions1. Is this happening to all the external domains (yahoo, aol etc).2. Is this happening to all the users?Some of the domians like yahoo and aol will not recieve your emails till the time you have reverse DNS configured on the DNS.Ask your service provider to create a reverse DNS entry for your domain.Raj

Hi, Thank you for you reply. 1. It's happening to 1-2 external domains. (edpnet.be and buchenwald.de) 2. When other users are trying to send a mail to this domain, they don't get through. I've found the mails in a "queue". Exchange System Manager - Administrative Groups - Servers - <server> - queues. They stand by SMTP Internet Connector (SMTPC) - Buchenwald.de (SMTP Connector) - protocol: SMTP - source: Default SMTP Virtual server - state: retry - number of messages: 5

Just check if they are accepting your emails. Try to drop an email with telnet and see if that works. Check if you can send emails to yahoo and aol.Also ask if they are rejecting your emails?Raj

They aren't accepting emails from some users. I can't telnet because ISP blocked port 25 (or 23) They are rejecting mails because our mailserver send an invalid helo. Is there a way to check the helo?