[exim] Recipient verify only for non-authenticated users

Hi folks,

The default Exim configuration has "require verify = recipient" in
acl_check_rcpt.

I'm having problems with Outlook users where they send a message to 20
people and the smtp session for the whole message gets rejected because
one message exhibits a temporary failure. The most noteable one is "host
lookup did not complete".

I was hoping to disable recipient verification for authenticated users
on the basis that these messages would go into Exim queues, be delivered
to valid recipients and the failed ones returned when the retry time
expires.

Can anyone suggest what is needed to modify the line to do this, or
alternatively a way to prevent the whole SMTP session from being
rejected when only one recipient gets this error?

Thanks,
Colin.