Porting MySQL's DESCRIBE and ENUM features

Hello,
 I'm helping to port some somewhere from MySQL to Postgres, and am
looking for an equivalent to MySQL's DESCRIBE function. Do you know of
one for Postgres? Specifically, one way DESCRIBE is used in this software is to get the
values from ENUM, where a MySQL column declaration might look like this:

ReceiveMail        ENUM ('Yes', 'No') NOT NULL DEFAULT 'Yes',
 I can get the same functionality in Postgres like this, but what can
use to get the values back of what's being checked? Thanks!

ReceiveMail        CHAR(3) check(ReceiveMail in ('Yes', 'No')) NOT NULL
DEFAULT 'Yes',
    -mark <<-------------------------------------------------------------->>
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