Postfix: SMTP: problem in a client like outlook

Hello,

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