WQWorkers are limited roughly to MAX_ARG_STRLEN (the kernel
limit of argv + environ) to avoid excessive memory growth.
Occasionally, we need to send larger messages via workqueues
that are too small to hit EMSGSIZE on the sender.
This fixes "lei q" when using HTTP(S) externals, since that
code path sends large Eml objects from lei_xsearch workers
directly to lei2mail WQ workers.