Outlook, as of 3 days ago, has not been sending emails.

There are no error messages and the emails are being put into the sent items folder but are not being sent.

We found out when people I have emailed called about not getting responses.

We have Outlook on 6 Macs, only two of them are doing this.

I have checked all the settings and passwords and everything is correct. I have been looking at trouble shooting and help files and cannot find any information on this or what to do. I have contacted my web mail server and the problem is not on there end - so they say.

Help!