Sending a welcome email to imported users

Through our LDAP connection all accounts created in AD are instantly created in ServiceNow. I had planned to leverage this process to send a kind of "Welcome" email to all new employees/students as they are added to the sys_user table, but I've hit a snag because even though their AD usernames are created their actual email addresses aren't created until midnight when a report is run somewhere by the AD admin and it creates an email account and attaches it to their username.

So what I need to do now is schedule something that checks for newly created accounts in the sys_user table and sends this "Welcome" email at like 4am everyday. I assume it needs to be done maybe through the event registry and the system scheduler, but I really haven't messed with those to features at all so I need some help...