New top domains

Dear Mj2 developers,

I have been managing my mailing lists with majordomo with many years,
the last four of them with majordomo 2. I would like to help with a
recent problem. One of my subscribers changed his mailing address to a
new domain, "xtec.cat". I checked and this new top domain, "cat", is
recognized by the domain name system. However, it is not recognized by
majordomo, and the subscription is denied. Could you tell me how I can
add this domain to the list of top domains majordomo recognizes?

Best,

Zvi.