Need help sending mail

[tel]

I'm setting roundcube up for the first time, and I'm running into a couple of problems.  My setup is that I'm running an IMAP server on my home machine using dovecot, and I send mail out using my ISP's (Comcast) SMTP server.

Postfix is set up to accomodate this, and when I send mail out using mutt, for example, it just works. 

Can't get roundcube to do this.  I am able to get my mail just fine, but when sending mail, nothing happens.  The message "Sending mail" shows up, but never goes away, and the mail is never sent.

I've played with most of the smtp settings in the roundcube configuration, but nothing seems to change.  So my questions are:

1. What is the proper way to set the roundcube configuration to just use the settings in postfix so that I can send mail out using Comcast's smtp server?  Should I set the smtp server to be localhost (my postfix), or do I have to explicitly set the smtp server to Comcast's settings?  Do I have to do something with sasl, which I had to do with postfix?

2.  3 different users have email accounts on my server, and their username/password for the server is different from their email login/password.  Therefore, using %u and %p don't work in the configuration script, and I can't hardcode the username/password in the configuration, because I have 3 users.  Is there a way to read a different username/password combination for sending mail depending on who is using roundcube?

[Yoni]

In this case you are using your Comcast Provider as relay. Postfix is sending messages just fine (as you mentioned) which means your relay has been properly configured in postfix.

Roundcube Webmail should use your localhost as SMTP. Message is passed to postfix and it further takes care of the delivery through your relay.

[tel]

Thanks!  I set the host to localhost, the port to 25 (I hope that's right) and my username and password to my Comcast username/password. Still wont send. Do I need to change the port or username/password (since postfix already knows this stuff)?

[Yoni]

You do not need to use your comcast username and password... You will use the username and password you have to authenticate to your MTA. So, your webmail login will be the combination used for sending as well...

Forget about the way the message goes out. That has been configured already and that takes place between Postfix and your relay (Comcast account).

Look only at your configuration between webmail and your email server in this case.

USER -> EMAIL SERVER -> Message goes to postfix.

POSTFIX -> COMCAST -> Message delivered to recipient.

If your message doesn't go through when webmail is configured to send through localhost is because either port 25 is wrongly specified and you need to use a different port depending on your configuration or the authentication method is incorrect. Either way, check your Server setup and forget how the message goes from postfix to Comcast because that's already working as you mentioned.