FIX: Outlook 2013/2016 - Email Address No Longer Valid

**Update thanks to anonymous commentor, this apparently works for Outlook 2016 also**


One of our users was getting an undeliverable message error in Outlook 2013 warning that one of the recipient's email addresses was "no longer valid" when sending mail to another particular user within the company.

The recipient was able to still receive the emails regardless, and the sender did not receive the error in the Outlook Web App.

This lead me to believe it was something local to the Outlook client, particularly related to the Autocomplete.

Tried removing the recipients address from the Autocomplete list to no avail.

After some research, tried this and it worked.

For Windows 7:

Turn off Outlook.

Open widows explorer and turn on "show hidden files"

Go to C:\Users\**USER**\AppData\Local\Microsoft\Outlook\Offline Address Books

and re-name the f[older] here (add "old" to the end).

Restart Outlook.

The user was then able to send mail to the recipient without the warning message.  We re-downloaded the Global Address Book and they were still able to send mail to the other user without error.

Source:

https://community.spiceworks.com/topic/397609-weird-email-issue-e-mail-address-is-no-longer-valid-using-office365?page=2

Global Address Book Not Available in Outlook 2013

Symptoms:  User cannot view shared calendars
                    Cannot check network address contacts / network address book not viewable
                    Outlook won't send email to contacts not in local Outlook email contacts address book
                    Offline address book for cached account was missing in computer files
                    User can send mail to network addresses in the OWA ("Outlook Web App") successfully

Solutions Attempted:

- Attempted to download the global address book from File -> Account Settings -> Download Address Book (default global address list did not show as an option to download)
- Shift + Ctrl + B to open the address book, did not show global address book in Address Book list or in Tools menu -> Options for address book
- Start -> Run -> Outlook /safe command to open Outlook in Safe Mode, but still showed same symptoms.

Resolution:

- Found a Microsoft article that directed me to delete a registry key.  Navigated to here for Outlook 2013:

HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Profiles\<profile name>

Then searched for the 001e660e registry entry.

Upon deleting this entry everything began working normally.

The user was then able to download the network address book, view shared calendars, and send mail to addresses in the global address book.


SOURCE:

https://support.microsoft.com/en-us/kb/3031401