I am unable to send emails (email is send but never delivered) using OWA, from different remote locations using different ISPs. When I send emails from these remote locations relaying over available ISP, emails are being sent just fine.
Where should I look for problems in Exchange settings
- accepted domains
- send connectors
- receive connectors.
Checking the message queue I have found the following error message
The message has been queued on server 'server.domain.local' since 2/26/2012 11:57:47 AM. The last attempt to send the message was at 2/26/2012 12:05:29 PM and generated the error '451 4.4.0 Primary target IP address responded with: "451 5.7.3 Require basic authentication." Attempted failover to alternate host, but that did not succeed. Either there are no alternate hosts, or delivery failed to all alternate hosts.'.
What could cause this problem?