Managing Active Directory does not always have to be complicated. If you are spending more time trying instead of doing, then it's time to look at something else. For nearly 20 years, AD admins around the world have used one tool for day-to-day AD management: Hyena. Discover why
Next time don't reboot whole server.
First restart GFI services if it not solves then SMTP service, if it not helps IIS service and at the end the whole server.