I agree with most of the above comments, and in particular, I would also stress how important it is to have "constant" data outside of your function.

Additionally, eliminating duplication is also a priority, though not at the expense of needless complexity. In this case, @SYS is really the same as keys %POvars, so there is no need for this extra definition.

Further along those lines, I would restructure your definition something like:

my @POvars_common = qw[ ppo userid email ];

my %POvars = (
        'GRP' => [@POvars_common, 'gwpo', 'gwdomain'],
        'JAG' => [@POvars_common, 'jagexcept'],
        'CIS' => [@POvars_common],
        'MST' => [@POvars_common],
        'GCG' => [@POvars_common]
);
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Although this doesn't seem like a big deal, removal of duplication can help with:

• Accidental transposition errors, such as one of your entries having 'emall' instead of 'email', which is hard to spot amidst many similar lines. Using Perl with the '-w' option, and use strict will spot errors in your variable names, but not your string constants, unless these happen to generate errors as well.
• Errors when changing the structure on a global scale, which requires modifications to every single entry in this case. This usually happens to every program, so plan for it in advance.
• Synchronization errors between needlessly linked data structures, such as @SYS and %POvars, where one has an entry which the other does not.