Sending e-mail in Kmail failed

I use gmail as my POP and SMTP with Kmail. This setup was working recently but does not work now. I can receive e-mails but can not send. I already checked all the settings for SMTP but they are all correct. How can I fix this problem? This is the error I get when sending email: Sending failed: Authorization failed, An error occured during authentication: SASL(-4): no mechanism available: No worthy mechs found authentication not supported The message will stay in the 'outbox' folder until you either fix the problem (e.g. a broken address) or remove the message from the 'outbox' folder. The following transport protocol was used: artjuera@gmail.com TIA I am sending this message direct from Gmail's web-based client.