You can't tell just by the fare class whether or not a fare is refundable as there are both refundable and non-refunable variants of most fares. On most purchases, unless you select the refundable option in search, it will present the non-refundable option and will give you the option to select the refundable variant of fare which will book into the exact same fare class. The "Fare Details:" line of email receipt will have the 8-letter fare basis codes encoded in it (which uniquely identify fares purchased) and the fare rules can potentially be retreived from EF if you also have date and origin/destination. Although generally refundability is encoded in the fare basis code itself and if we knew route and fare basis code it will likely reveal whether or not the fare was refundable.