this will now return the result of the last contactGroupToLDIF call -- so, if contactGroupToLDIF returns false for any element but last of the list, the result is still true (like the current code, though)

IMHO there are two options:
a) if the results of the various contactGroupToLDIF is not wanted/needed, cast them to (void)
b) if the results matter, either make sure that at least one failure generates a failure result of the whole function, or stop and fail at the first contactGroupToLDIF call that returns false

ditto

right. my reason for this bad code was that I was following other patterns in the file.
for example, see LDIFConverter::addresseeAndContactGroupToLDIF()

I think the return value should matter and we should do:
result ||= contactGroupToLDIF(*it, str);

except I don't know what that will break.
I will try that and see if at least the unit tests still pass

You could simplify by using result |= contactGroupToLDIF(*it, str)

I could. but I don't want to :)
if you insist.