Updated to be about the newer Azure sync crap.
If you have "no heartbeat" or "No recent password sync" -
Seems every time this dung heap software stops syncing password it is 1 of 2 options:
1. They are having an outage.
2. The sync server needs a reboot.
Just reboot the sync server as a first option and recheck service status on the web side of this abomination.
Here is their article on the same, but trust me, just reboot the sync server: https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-troubleshoot-password-synchronization
that is all....
Say you wish to add an alias email to a user in your Exchange Online.
Go ahead, give it a shot, I will wait.....
Ok, you figured it out by now.
adsiedit.msc
Find the user
find the property proxyAddresses
Edit it
fill in the address in the format:
smtp:email@domain.tld
If you have multiple, and want one to be primary, add SMTP: (note upper case) to the primary email address.
Use lower case smtp on the non-primary alternate email addresses that the user should receive.
Oh, yeah. Now push your sync as you don't want to wait 3 hours:
cd "C:\Program Files\Windows Azure Active Directory Sync"
DirSyncConfigShell.psc1
And type:
Start-OnlineCoexistenceSync
Now, simple as pie, verify it worked using:
"C:\Program Files\Windows Azure Active Directory Sync\SYNCBUS\Synchronization Service\UIShell\miisclient.exe"
Easy, is it not?
Pretty schweet eh?
Yes, I cursed the same way as you are just now :-)
ADUAC will catch up to some day, just you wait... hardy, har, har...
Thanks to "Tech" at emtunc.org for that one:
http://emtunc.org/blog/08/2011/using-adsiedit-to-add-or-remove-e-mail-aliases-on-on-premises-active-directory-office-365/