Emails remaining in outbox when attempting to send.

Hi all,

i have two older iMac’s (late 2009) and up until a few days ago everything was working as it should. Although now both computers aren’t allowing emails to be sent and the emails are remaining in the outbox. I’m not a very technically minded person, have basic knowledge hence why I’m asking for help here. The emails are sending through iPads and phones so it’s not the internet or the email providers (I think). Any help would be greatly appreciated.