The EXPN command/verb can be asked to respond in several ways.
EXPN
Calling the EXPN command with no arguments or an invalid mailing list name will cause it to return an error.
>>> EXPN
550 Not authorised
>>> EXPN some-list
550 Not authorised
You can also explicitly tell EXPN to fail by passing fail= as part of the mailing list name.
>>> EXPN fail=test-list
550 Not authorised
EXPN mailing-list
Three lists are built-in to Blackhole for use.
list1, list2 and list3 and can be used as follows.
>>> EXPN list1
250-Shadow <shadow@blackhole.io>
250-Wednesday <wednesday@blackhole.io>
250 Low-key Liesmith <low-key.liesmith@blackhole.io>
>>> EXPN list2
250-Jim Holden <jim.holden@blackhole.io>
250-Naomi Nagata <naomi.nagata@blackhole.io>
250-Alex Kamal <alex.kamal@blackhole.io>
250 Amos Burton <amos.burton@blackhole.io>
>>> EXPN list3
250-Takeshi Kovacs <takeshi.kovacs@blackhole.io>
250-Laurens Bancroft <laurens.bancroft@blackhole.io>
250-Kristin Ortega <kristin.ortega@blackhole.io>
250-Quellcrist Falconer <quellcrist.falconer@blackhole.io>
250-Virginia Vidaura <virginia.vidaura@blackhole.io>
250 Reileen Kawahara <reileen.kawahara@blackhole.io>
EXPN all
The all argument combines all three lists and returns them.
>>> EXPN all
250-Jim Holden <jim.holden@blackhole.io>
250-Naomi Nagata <naomi.nagata@blackhole.io>
250-Alex Kamal <alex.kamal@blackhole.io>
250-Amos Burton <amos.burton@blackhole.io>
250-Shadow <shadow@blackhole.io>
250-Wednesday <wednesday@blackhole.io>
250-Low-key Liesmith <low-key.liesmith@blackhole.io>
250-Takeshi Kovacs <takeshi.kovacs@blackhole.io>
250-Laurens Bancroft <laurens.bancroft@blackhole.io>
250-Kristin Ortega <kristin.ortega@blackhole.io>
250-Quellcrist Falconer <quellcrist.falconer@blackhole.io>
250-Virginia Vidaura <virginia.vidaura@blackhole.io>
250 Reileen Kawahara <reileen.kawahara@blackhole.io>