I have good experience for two similar sized (even larger) institutes where I simply put a minimalistic issue tracker (Redmond, Trac, OTRS) behind an E-Mail Gat

I have good experience for two similar sized (even larger) institutes where I simply put a minimalistic issue tracker (Redmond, Trac, OTRS) behind an E-Mail Gateway. Since email is still dominant in the traditional world of academia, sticking to an address support@institute.example.com is a no brainer. Having said that, my recommendation would go with OTRS.