Apple Mail using El Capitan I receive incoming emails   but cannot send out.  They stay in the 'Out' box.  In Mail Preferences   it says  'Outgoing Mail Server (SMTP)   -  in the slot is 'concordmedia.org.uk    I am using  IMAP system.
Not a lot to go on, but here are the steps I follow:

https://support.apple.com/en-us/HT204075

Is there a guide from your organization that explains how to configure Apple Mail or even a configuration profile so you can enter the settings perfectly without having to enter them manually?