Postfix: SMTP: problem in a client like outlook


I set up a mail server, here quickly, his tree:

  • Postfix,
  • Procmail + Spamassassin + ClamAV,
  • Dovecot (POP and IMAP).

Everything is working properly, in fact, I receive many messages in my mail box, I am able to send email, but only from a webmail as squirremail or via usermin.

The problem occurs when configure my mail in a mail client, as outlook:

  • The receiving server (or pop imap) is detected and the receipt of the message works well,

- The sending server is not detected, I try with or without authentication, it does not work.

I would like to know if there is a particular setting to allow connection to the sending server (SMTP)?

For info, ports imap/imaps, pop/pops and SMTP (25) are open.

Thanks in advance