Just some feedback to benefit others with this very vexing problem.

The solution I found by trial and error after weeks of thrashing around more less matches the others here.



I moved from Windows XP to Windows 7 64-bit using PCMover and, because my trusty Outlook 2003 would no longer work with 64-bit I installed Outlook 2007. I started getting the problems mentioned here (Your message did not reach some or all of the intended recipients....etc. etc.). To compound my puzzlement, each time the error arose I discovered that Outlook had changed the account from which the message was sent.

I tried reinstalling Outlook 2007, deleting and reinstalling accounts, etc. etc. etc. and nothing worked. Then, each time the error came up I opened the adressee's file in Contacts and retyped the email address. This was a bit of a slog, of course, because if the message had been sent to 8 people, for example, I didn't know which address to change so I had to go through and change them all.

Anyway, the problem seems to have stopped but, as someone else said here, it is annoying that one doesn't know how it arose. It seems that when the Outlook addresses are transferred to the new installation in Windows 7 some of them become corrupted in a way that makes Outlook (a) change the Sender account and (b) throw up this error message.

I'm also very disappointed with Microsoft for not having a paper on this problem which, it seems, has been known - together with its solution - for quite some while.

Paddy

I am still having the odd lesser used email addresses rejected 4 months on, for the same reason and in my case, take a note of all the address data, delete the contact, and then enter it all afresh.
I love Win 7 (it is what it should have been after XP) but am totally exasperated that Microsoft can't sort this out and at least acknowledge that there is a problem. I wonder if it will still be there with Outlook 2010?
One more reason to go Apple next time.

Unfortunately the answer is YES! MS-Outlook 2010 DOES exhibit this rather annoying problem.

And YES, the "fix" seems to be to go into your contacts, delete the email address of the contact bouncing back (the "Display As" field should automatically be deleted). Re-enter the email address from fresh. The "Display As" field should read "Contact's Name (contact@emailaddress.etc)." Save and Close contact.

Once you have done this, you will be able to accept quick-recommendations from Outlook for that contact in the "To:" bar just by typing the first few letters of their NAME. You will note that whereas before the quick-recommendations only showed an email address (and were undeliverable), it now shows "Contact's Name (contact@emailaddress.etc)." It seems, perhaps, that Outlook was unable to cross reference a quick-select email address alone with the Contact's info stored in the address book, whose entry is based on Contact's name as stored in the database.

As for why mine started doing this all-of-a sudden? I am no techhie, but my problem began after syncing my contacts to my new HTC Desire cell phone (running Google Android 2.1). My guess is something got corrupted in that process. HTC Sync is buggy as hell. The software engineers must have cut their teeth programming for Microsoft.