We had an old Exchange server that was having many issues. Probably because it was on a box that was maxed out and hitting 100% usage on the hard drive and memory for quite some time. Rather than migrate some of these issues to a new server I just decommissioned the old server and started from scratch on a new 2013 Exchange server. I recreated the email addresses, exported and reimported mailboxes, etc. Everything seems to be working great except some internal email get's bounced, I've seen this before and usually just deleting the email cached address and typing them from scratch cleans it up. However that only partially works here, And it's hit and miss, Sometimes it works and sometimes it get's bounced back. And there doesn't seem to be a pattern, Sometimes new emails work and sometimes they get bounced.
I'm thinking there must be some additional cache file that I don't know about. Any ideas?