Q0633
Question
Why is $domain not set in the smtp transport?
Answer
The smtp transport can handle several recipient addresses at once. This happens by default if the host lists for the addresses are identical. A single copy of the message is sent, using multiple <small>RCPT</small> commands to transmit multiple envelope recipients. The $domain variable is set in the smtp transport only if all the recipient addresses have the same domain. You must have a case where several addresses with different domains resolve to the same set of hosts. If you want to restrict the transport so that it handles only a single domain at once (but still possibly with more than one recipient), set
multi_domain = false
If you want to restrict the transport so that it handles only a single address at once, set
max_rcpt = 1