Outlook 365 problem

Hoping someone can help but not expecting it.

Background. I had a perfectly working Exchange server with Outlook 365 connected to it working perfectly. Sometimes when my DNS server went down for updates Outlook could not connect because it could not find the internal name and would find my external name. It would try and fail at this and then it would go to Outlook.com and connect with that. From then on everytime I would use Outlook would get a message that mailbox had been temporary moved. Only way to fix was to delete the profile and start again.

So I put a outlook.com in my hosts file to 127.0.0.1 to stop this and it worked.

Two days ago had the same thing but it still managed to get to outlook.com somehow and cock up my profile. Deleted it and now when I try and create the profile I get an error that the name cannot be matched to name in address list.
Googled this and all the answers point to exchange being the issue and I spent hours finding out why with no success. My iPhone and iPad both connect to exchange fine, OWA works fine so nothing appears wrong with the actual mailbox. They say autodiscover is the issue.

However last night I tried it from my Windows 7 machine with Office 2013 installed and Outlook 2013 went through the wizard and connected with the mailbox fine.

Clearly this is an Office/Outlook 365 issue but just what the issue is and how do I reconnect the profile?

Also how did Outlook manage to get past the hosts file and connect to outlook.com again?

Any help at all welcomed.

Okay just found some more info and some guy reckons it is active directory that is the issue. From his web site

After Active Directory replication the LegacyExchangeDN look like below,
LegacyExchangeDN : /o=ORG/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=Bolden, LaRhonda

His original had some numbers after the LaRhonda.

Looking at mine it has the following

/o=xxxxx/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=4e74e3ae6bf7410db4a56fd34a7a21a1-John Veldthuis

Do I edit this in ASDI Edit and get rid of the long number? I know using ASDI Edit can make things go bad very quickly.

Well fixed one problem and got another. I deleted the windows credentials for all microsoft stuff and anything to do with mail. There was about 5 deleted.

This allowed me to reconnect with the exchange server after asking for my credentials about 12 times.

Got Outlook back but now it continually asks me for my credentials even when I tel it to remember them.

Man what a shit bit of software microsoft has made Outlook into.

Okay think I finally have it but man shocking way things go.

First going to outlook.com without permission or asking to. Bad nono and will look at the firewall to stop it even further.

Next a working system taken down by a minor issue and having to delete many credentials to get it back.
Finally the non-stop asking for credentials once I had it working. This was cured by clicking cancel on the request which then caused outlook to say it needed a password. Clicked on that and it connected without asking for a password and have not been bothered since.

Are the mailboxes and server on prem and do you manage them? Is it a local deployment or hybrid?