Forwarded message size

When I forward a message with a 15mb attachment to multiple recipients it ends up as a 40mb size and is rejected by my server. If I open it in the outbox it shows 40mb but after clicking send again its size is reduced to 24mb and sends OK. This only started after updating to V8 I am now running 8.1.852 (333c574)

The following reply by @Son-of-A-Gun may be of help: