During actual use, the perl function in question cannot open the file
it needs... but during exim -bt, it opens it fine.
WHY oh why would this happen. It makes zero sense to me. Might exim
run with different permissions between -bt and -bh, or between
verifying and actual sending?
And the only difference between the two .confs is require verify =
sender. The same function has to run in both cases, and succeeds in
one yet fails during the other.