Here are the first two of my three questions:

     1) What is the oldest version of Apple's OS X Mail email client application that Exchange Server 2013 supports for setting up an IMAP connection (as opposed to an POP or Exchange connection)?  

     2) How about Exchange Server 2010? 

I would assume that the answer to both questions would be "ANY version of the OS X Mail application would be supported by Exchange Server for IMAP connections ", given that ALL versions of OS X Mail support setting up IMAP4 client accounts, and both Exchange Server 2010 & 2013 support IMAP4 clients.

However, I know from recent experience that my employer's Exchange email hosting service works fine when I set up OS X Mail IMAP accounts on Macs running OS 10.6 or later, but NOT when I try to set up OS X Mail IMAP accounts on Macs running OS X 10.5 and 10.4.  

Sometimes, the OS X 10.5 / 10.4 setups proceed okay up to the synchronization phase (i.e. after the account has been created and the Exchange server transfers the server's contents to the newly-created, empty client account).  However, invariably the synchronization is continually interrupted by OS X Mail prompting me to re-enter my credentials to log back into the incoming mail server to continue the server-client synching.   When I re-authenticate, the synchronization precedes but then a minute or two later I get another credential prompt.  This pattern continues until the client's credential prompt dialog box no longer accepts my username / password info and quits the synchronization process altogether, forcing me to delete the client's IMAP account and start from scratch with a new account set up attempt.  The farthest I ever got to completing an IMAP account setup on OS X 10.5 and 10.4 versions of OS X Mail is about 80 percent of the synchronization being completed before the Exchange server's IMAP incoming mail service becomes inaccessible to the client. 

Other times I will complete the OS X Mail IMAP account set up but then the synchronization doesn't even begin at all because I'm immediately prompted for my credentials and every time I submit them I'm prompted again (as if I'm entering the wrong username and password when I know for a fact that I am entering the correct information).

I should make it clear that the problems I've had with the "Exchange as IMAP" client account setups in OS X 10.5 / 10.4 versions of Apple Mail occur EVEN when I start with a fresh OS X software build -- i.e. a startup disk that has been installed from scratch using an OS X installation DVD, thereby essentially ruling out any contributing factors on the client side (in part because the OS X Mail client app is being set up for the first time).

In closing, here's the last of my three questions:

     3) Is there any official documentation published by Microsoft that addresses this issue (e.g. a list of the versions of OS X compatible and "IMAP-capable" email clients such as Apple Mail, Thunderbird, etc. that are guaranteed -- at least in principle -- to be supported by Exchange Server for setting up a reliable, fully functioning IMAP connection?)

Thank you in advance for your consideration of my three questions and for any answers offered.

Hi Jim,

Depending on the customer feedback, it works fine. Apple Mail the client that comes with OSX supports standard protocols (POP3, IMAP, SMTP), these are all supported by Exchange 2010. 

If you're running Mac OS 10.4 Tiger or Mac OS 10.5 Leopard, you can still use the Mac Mail App to connect to your account. However, you need to connect to your account without using IMAP or POP.
If you're running Mac OS 10.6 Snow Leopard or Mac OS 10.7 Lion, you can use the Mail program included with those releases to connect to your email account automatically using an Exchange account.
When you use Mac OS 10.6 Snow Leopard or Mac OS 10.7 Lion and connect using an Exchange account, you can use features that aren't available to users who connect through IMAP or POP, including iCal and Address Book.
More details about Set up email in Mac OS X Mail, please refer to:
https://support.office.microsoft.com/en-in/article/Set-up-email-in-Mac-OS-X-Mail-de372dc4-9648-4044-a76c-e8a60e178d54?CorrelationId=a0ce4c19-1492-4e3b-bc7e-4af83d3cb347&ui=en-US&rs=en-IN&ad=IN

Additional, I find a similar thread about your question, for your reference:
https://social.technet.microsoft.com/Forums/exchange/en-US/b112b61e-401f-4ad9-b459-a25673ff5407/connecting-to-exchange-2010-using-apple-mail?forum=exchange2010
https://social.technet.microsoft.com/Forums/en-US/d3c9b4ad-822b-4a7c-88b8-39df3f166f96/how-to-setup-exchange-account-on-macbook-os-x?forum=exchange2010

Best Regards,
Allen Wang

Hello Allen -

Thank you for your reply.  

I want to emphasize that the problems I am having setting up my Macs to access Exchange Server occurs when setting up OS 10.4 & 10.5 versions of Apple Mail using an IMAP connection (i.e. I'm not trying to set up an Exchange connection or some other connection that these older versions of Apple Mail don't support).  

Moreover, the procedure I am following to set up these IMAP connections is exactly the same as the "Set up POP or IMAP on Mac OS X" procedure outlined in the "Set up email in Mac OS X Mail" article you linked in your reply.

Is there anything my email hosting service could have done in configuring their Exchange Server that would cause IMAP connections to be fully functioning and reliable for versions of Apple Mail running on Mac OS 10.6 and higher but NOT for Apple Mail running on Mac OS 10.5 & 10.4? 

- Jim

• Edited by Jim_314 3 hours 17 minutes ago