[Dovecot] Auto logging-out client

[Nicolás]

Hi list!

I'm writing because of an issue I'm having with my Postfix-Dovecot 
installation. Everything's working fine but when an IMAP client is idle 
for some time, Dovecot automatically logs it out.

Jul 26 14:01:16 mail dovecot: imap(nicolas at devels.es): Disconnected: 
Logged out bytes=1271/7439

This entails errors when trying to send e-mails after this auto logout, 
such as:

host devels.es[91.215.158.237] said:
     550-Please turn on SMTP Authentication in your mail client, or 
login to the
     550-IMAP/POP3 server before sending your message.

Which result in a very annoying and continuous proccess of restarting my 
mail client.

Is there a way to avoid this auto-logout, or at least configure the time 
after I want idle clients to auto-logout?

Thank you very much!

Nicolás