This is one of Exim's more cryptic errors:
Mar 29 11:22:52 114075-web1 postfix/smtp[20589]: 9E0142FC589: to=
When you send e-mail to an Exim server with a sender verify callout enabled, the Exim server will connect back into your server and verify that your server accepts mail for the sender's e-mail address. For example, if you send e-mail from orders@somehost.com, the Exim server will connect back into your server and do this:
HELO someotherhost.com
250 somehost.com
MAIL FROM: test@someotherhost.com
250 2.1.0 Ok
RCPT TO: orders@somehost.com
250 2.1.5 Ok
Exim will make sure that it gets a 250 success code before it will allow the e-mail to come into its server. Some situations that cause problems with this process are:
- Port 25 is blocked inbound on the sender's server
- Something else is filtering port 25 inbound on the sender's server
- The sender's server uses blacklists which delay the responses to Exim's commands
The most obvoius problem is missing:
If the sender is using sender callout verify himself, the verify will never succeed as the verification targat wants a verification from the verifier first.
Besides it can be used conveniently for DOS attacks.
This is why sender callout verification should NEVER be enabled (and not even offered by EXIM)!