Forgot to say that the corollary to the OP's original question: -- list of airports that cannot process e-ticket -- would be a different list for each OW airline. What a mess! And with major cities like HEL on the list, you cannot really know. I wonder if the e-ticket issuing software can be relied upon to have the correct list, and not issue you an e-ticket for a flight sector which can never use it! I presume it can, but something to worry over. In any case, when traveling with an e-ticket, always have your ticket number with you (not just the PNR). Twice I have been refused passage on an e-ticket until I could product the ticket number (for some reason the e-ticket was lost in the system but could be located using the ticket number; if I did not have that info I would have been denied boarding or required to purchase another ticket). Needless to say there is no provision in the CofC for denied boarding due to airline error in processing the e-ticket; apparently the airlines have succeeded in shifting all the risk to the passenger.