Added 24 years ago with Outlook 98, only the second version (Outlook 97 was the first one). By that time scale it could hardly be called an afterthought.
Yes I deployed/supported many hundreds of Outlook installs back then, as well as Exchange servers, and I taught classes on using Outlook to companies that had Exchange installed.
"Outlook 97 is an ENTEPRISE GRADE email client. It is primarily intended for use with Microsoft Exchange Server"
Microsoft Outlook (not to be confused with Outlook Express) is an enterprise grade e-mail client. It is primarily intended for use with Microsoft Exchange Server. It was available as both a stand-alone product and as part of Microsoft Office.
winworldpc.com
Microsoft has the basic email clients ..starting with Outlook Express, and onwards, to be used with residential email (pop/imap)...and they work quite well. As well as the plethora of 3rd party email clients out there which work very well with pop/imap.
If you gather a lot of "experienced" IT people in a room and start talking about Outlook, and IMAP, you'll get a lot of moans and groans, if not a bunch of sarcasm asking why you want to do that. You'll never get 100% of a group of "experienced" IT people saying Outlook <==> IMAP is a good idea. Sure you can find some who have not run into problems, I guarantee they don't have a large client base to base from...that's why I say if you gather a room full of "experienced" IT people...
Yes, we know that you can connect Outlook with GMail or <insert your ISPs freebie email>, etc.
But...most of us also know that, over time, you'll have to battle with Outlook and it's connection to that mail system, due to some error. Google often makes subtle changes to their email system and its protocols...and that can break Outlook. Outlook also gets cranky with larger mailboxes if they're IMAP.
To me, if ones email setup requires frequent attention to troubleshoot...it is not a good choice of an email system.
To me, one should spent something like 30 seconds to configure an email account, and then it's rock solid from that point on. Someone should not have to keep calling some IT/computer person to keep troubleshooting every several months or every year or so.
Part of the job of an IT person it to guide the client into a good reliable choice for a system, "things that work well". I wouldn't feel right recommending a system to a client...knowing that system was not good.