help with sed-friendly regex with negative look-ahead syntax for sendmail

So the below regex (the left side in bold) does not seem to work in sendmail's R & K commands. I’m trying to allow emails from cities and schools that have email addresses that look like:
[email protected] or [email protected]. It seems that negative look-aheads are not supported. Would anyone have any idea on how to make this sed-friendly syntax? Note that the right side (unbolded) works fine by itself.
(?!.*\@ci\..+?\.us$)(?!.*\@*\..+?\.ny.us$)[a-zA-Z_0-9.-]+<@[a-zA-Z_0-9-]+?\.+[a-zA-Z_0-9.-]+?\.(us|info|to|br|bid|cn|ru)


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