callout and save the result in the cache for next time, unless no_cache is set,
or unless we have a previously cached negative random result. If we are to test
with a random local part, ensure that such a local part is available. If not,
callout and save the result in the cache for next time, unless no_cache is set,
or unless we have a previously cached negative random result. If we are to test
with a random local part, ensure that such a local part is available. If not,