Sometimes, the IRS is pretty lazy. They may want you to fax it to them. Think long and hard about whether their ability to have access to the documentation without a subpoena was intended to make it the equivalent of ordering a pizza.
In my bank they would:
* show up in person,
* present their credentials and a letterhead request indicating this agent was sent to pick up the supporting documentation on SAR DCN # XXXXXXXX.
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.