Sending Messages Problem

We have configured Outlook 2003 to receive and send
messages from two different ISPs/Mail Servers. We needed
to do that to receive mail using our domain holder's
incoming email and to send out using the cable company's
(Comcast) connection. In our small network some computers
are able to send email OK, others are not able to send
email. The emails just stay in the outbox and there are
no error messages. All incoming messages come to all
computers OK.

We think we have the same settings on all computers, but
there must be some differences somewhere. The Outlook
Mail account settings are definitely the same. Any ideas
on why we are not able to send messages from some
computers.

This is a new network just installed in a new office with
Windows XP Professional and Office 2003 in each
computer. Internet access is through a cable modem.

Thanks,
John

Follow on to original message:
We have found that the outgoing messages don't get sent
when the SEND box is hit, but while the message is in the
outbox waiting to be sent, selecting SEND/RECEIVE will
send the message--only the message in italics, not the
other messages that have been there awhile and not yet
sent.

The setting to 'send immediately when connected' in email
setup is selected on all computers. Is there another
setting to look at that pertains to having messages sent
and received immediately, rather than waiting until
SEND/RECEIVE is selected?

Any help will be greatly appreciated.

John

-----Original Message-----
We have configured Outlook 2003 to receive and send
messages from two different ISPs/Mail Servers. We needed
to do that to receive mail using our domain holder's
incoming email and to send out using the cable company's
(Comcast) connection. In our small network some
computers
are able to send email OK, others are not able to send
email. The emails just stay in the outbox and there are
no error messages. All incoming messages come to all
computers OK.

We think we have the same settings on all computers, but
there must be some differences somewhere. The Outlook
Mail account settings are definitely the same. Any ideas
on why we are not able to send messages from some
computers.

This is a new network just installed in a new office
with
Windows XP Professional and Office 2003 in each
computer. Internet access is through a cable modem.

Thanks,
John