Tax advice: US citizen residing in foreign country.

I am helping my son do his taxes. He lives in a foreign country with questionable mail service. I am trying to e-file his tax. But there is no way to indicate a different mailing address (our home address in the US) from his residential address in this country. So now if the IRS were to send him a letter it has to go to his residing country. Previously I paper file and attach a note indicating a different mailing address. How can I do this thru e-file?
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