this can be done via spell if you interested,
mod file will be:
MODIFY cr PRE_VALIDATE z_trunc_desc() 1337 FILTER ((EVENT("INSERT"))&&(created_via=<email_method_id_here>));
spl:
cr::z_trunc_desc(...) {
if (strlen(description)>4000) {
send_wait(0, this, "call_attr", "description", "set_val", substr(description, 0, 4000));
}
}
remember to define correct creation method id,
sorry if there syntax errors presented cause i'm outside of the office