miconda left a comment (kamailio/kamailio#4290)
The sanity module does not drop the message unless is configured so. Furthermore, all the tests of sanity module are configurable, it is config writer choice to do one or another.
You can set the body as you wish with the functions from the textops/x modules. There is a transformation that can be used to extract how many characters you want from a string. You can do conditions on `$cl` and `$bs` and decide what you want to do.
This is one of most powerful/appreciated features of Kamailio over the years: ability to be flexible in receiving SIP traffic so the config writer can fix messages sent by broken UAs. It offer tools/components that enables it to be compliant as much as possible, but it is the matter of the config writer to make it so, when needed/wanted.