The Securities and Exchange Commission (search) has asked the New York Stock Exchange (search) to use keywords to search NYSE employee e-mails dating back to 2000, hunting for evidence tied to its ongoing Big Board probes.

The multiple investigations are looking at the outrageous pay package given to former chief Dick Grasso (search) — including how his compensation was determined and whether he exercised improper influence over those who voted for his pay — as well as taking a larger look at the quality of regulation at the Big Board.

The more targeted e-mail hunt comes as SEC gets closer to concluding its probes of the NYSE, sources told The Post.

As part of those investigations, the SEC last fall requested all of Grasso's e-mails, as well as those of his former assistant.

The agency later asked to review the e-mails of a number of top executives in market surveillance and requested the keyword search.

Officials from the SEC and the NYSE declined to comment.

While the SEC is jointly investigating the issue of Grasso's compensation with New York Attorney General Eliot Spitzer (search), it is also investigating how effectively the NYSE has operated as a self-regulatory organization.

The SEC is unlikely to join Spitzer's suit over Grasso's compensation, since the New York Attorney General has jurisdiction over New York not-for-profit institutions. The SEC, by contrast, has jurisdiction over whether the NYSE broke any securities laws.

SEC officials have not made a final decision about pursuing a suit against Grasso, say sources there who asked not to be named.

The SEC played a critical role in the ouster of Grasso. SEC Chairman William Donaldson first requested details of Grasso's pay last summer; the SEC boss was "furious" upon learning the details of Grasso's $139.5 million deferred compensation and retirement package, say people close to him.

The SEC immediately began an investigation into how the pay package was determined.

Meanwhile, the SEC's conclusions about the NYSE's regulatory effectiveness could be critical in determining whether the exchange remains a self-regulatory organization, supervising its trading floor and regulating its member firms.

A number of SROs, including the NYSE and the American Stock Exchange, have suffered massive self-regulatory failures. The SEC intends to examine the issue of self-regulation soon after it reworks the complicated rules surrounding market structure that will significantly impact every exchange.

NYSE CEO John Thain has expressed support for maintaining the current SRO model.