Certainly not anything that kids should be viewing.
However, the warning/language used DOES make sense to me. In email #1, "Girls doing lesbian acts" could be kissing, hence the need to clarify that it is sexually explicit, because kissing isn't sexually explicit. In email #2, pussies wide open gaping with jizz already implies that it is sexually explicit, so it would be redundant to add that in the subject...
