the instructions are in fab's release thread. here, let me google it for you:
apex 1.3 rom universal inbox - Google Search
the first hit is this:
[ROM] ApeX 1.3.0 for Droid X - Running, running, as fast as it can - Page 19 - Droid Forum - Verizon Droid & the Motorola Droid Forum
and the first page contains these comments from fab:
QUIRKS
-The Blur Email app (default email app) will FC if you do not have an account added through My Accounts. Just add an account first.
-If you have multiple Email accounts using the Blur app, you'll need to restore the universal inbox:
Code:
su
sys -rw
mv /system/app/Messaging.bak /system/app/Messaging.apk
sys -ro
sync
it worked for me, however i installed Handcent to mannage my texts as the Blur app didn't seem to be working. i've since discovered this thread (again, through google), which might offer a fix for the texts issue as well:
http://forum.androidcentral.com/motorola-x-roms-hacks/43211-what-aosp-experience.html
which contains this post:
OK I pushed back all these and now have the blur tex, accounts and email in the accounts working.
Push back with terminal with the apk files on your sd card
Universalinbox.apk
Conversations.apk
Messaging.apk
Bluremailengine.apk
BlurSNMessagingEngine.apk
BlurEmail.apk
__________________
hope this helps.