This is not necessarily the situation every time, but in the case of: Affected User #1: She uses OLK 2010 (will check patches and fixes today), and the person that consistently replies back to her is on OLK 2007. In another instance, the person replying to her is on OLK 2010 just like her. Affected User #2: He uses Entourage 2008 for MAC and the person that replied to him is on OLK 2010. Still having a heard time making sense out of this. Are you saying that the issue is from the OLK 2010 users? ~m

I think this was the fix for the issue I remember.Sukh

we thought this was just happening to one mailbox/user, but we now confirmed at least two users. it does not happen all the time, but when people reply to the affected users emails, the affected users email address appears "something" like this: '/O=DOMAIN/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=RECEPTION' From within our organization/company we are all on the same Exchange server and we seem to be receiving it fine despite the weird appearance of the email. However, aside from it looking weird and not right, our other concern is how it looks to people outside our company and those not on an Exchange server...We fear they might not be able to email us if the recipient's email looks like that when they reply. Thank you. ~m

That's an x500 address, check the primary email address for those accounts.Sukh

Already did. The primary is set for SMTP that is associated with the correct primary email address of reception@domain.com (sample).

Are you using Outlook 2010? Sukh

Mixed environment. One of the affected users is on Entourage 2008 for MAC, and the other is on Outlook 2010. Other users are on Outlook 2007 and some use OWA. ~m

I know there was an issue similar to this with Outlook 2010 which was addressed in SP1 and post fixes from Dec 2011. not sure if this happens only wiht OLK 2010 or with other too?Sukh

Hello, Did you check this in OWA? Maybe you can try to reply the affected users' emails in OWA, then check whether this issue will occur or not. Thanks, Evan Evan Liu TechNet Community Support

Hello, do you have migrated your environment recently? There might be a problem with the AutoComplete cache. Please clear it and then try it again. Greetings, Toni