Users did not receive Welcome Email to setup their accounts

What is their status when you look at the User list?
If it’s grey then you should be able to resend invite. 

If it’s red there are 2 possibilities - select the user and click on “Send Invite”. If it’s not working, then click on “Enable”. One of these should work. 

If their status is green, you can’t send an invite.

The status is for the user is Green but when I checked the users email for any emails from RingCentral there wasn't anything received. 

I am guessing you have selected “Activate by assigning credentials” as a Setup option when creating the users. This setup option does not generate any emails, regardless of SSO or not.

Shouldn’t be an issue, because you could easily write a Welcome email yourself… or let me put it this way - why is it an issue for you that a Welcome email was not sent, so that we can suggest a workaround?

The only reason whys it was a problem was because the first thing our trainer from RingCentral informed our users was that they would have received a welcome email from Ring to set-up their account set voicemail pin etc.. but as this welcome email was not sent it confused our staff and I wanted to know why they didn't receive a welcome email.