Thank you, Nick, for your answer. My apologize for not being too specific. My Exchange is on a separate machine, running on a NT 4.0 SP6. The Exchange server is published using the Secure Mail Server Wizard, I have some DNS filters, but only for TCP. Shall I have also for UDP defined one filter for DNS ? Or just UDP ? I noticed this last piece of information, after reviewing my ISA configuration VERY thoroughly. Regards, Alin