expensive_batch_assessment — only treat messages as different if the headers are rendered differently
expensive_batch_assessment = false
When looking for messages that can be delivered as a batch, Momentum checks the headers and bodies of every MIME part of messages that were submitted as a batch—a batch being one transaction with multiple RCPT TOs. Normally, if the bodies or headers have been modified since reception, the messages are treated as different. Enabling
expensive_batch_assessment renders the headers from each message to strings, and compares the strings, only treating the messages as different if the headers render differently. This enables messages with (identical) header modifications to be sent out in a batch, at the expense of more CPU load and IO. You should only enable this option if you are doing header modification using Sieve
ec_header_add or DKIM signing, for example, and you want batched outbound delivery to continue to work despite this.
The default value for this option is
expensive_batch_assessment is valid in the global scope.