Pop3 and client certificate

Hi!I have x.509 certificate based authentitication for web users, but i can`t setup this for pop3 users.

Any mail clients (outlook,thunderbird,the bat) ask me for password ?!

Outlook Express:

Server Response: ‘-ERR Unknown command: “USER”’, Port: 995, Secure(SSL): Yes, Server Error: 0x800CCC90, Error Number: 0x800CCC91

Thunderbird:

0[c50b80]: Entering NET_ProcessPop3 74

0[c50b80]: POP3: Entering state: 1

0[c50b80]: POP3: Entering state: 2

0[c50b80]: POP3: Entering state: 4

0[c50b80]: RECV: +OK CN=Alexey Ivanov/O=blablabla/C=RU has 79 messages (2487995 octets).

0[c50b80]: POP3: Entering state: 29

0[c50b80]: SEND: AUTH

0[c50b80]: Entering NET_ProcessPop3 30

0[c50b80]: POP3: Entering state: 3

0[c50b80]: RECV: -ERR Unknown command: “AUTH”

0[c50b80]: POP3: Entering state: 30

0[c50b80]: POP3: Entering state: 31

0[c50b80]: SEND: CAPA