Use Outlook from Office 365 to connect to another email server provider

We are in the process of migrating our emails from a third-party company to Office 365.  In the mean time, we are trying to set up some workstations with Windows 10 and Office 2016.  We decided to use one of our Office 365 licenses to download Office to one of these Windows 10 workstations.  Before we are ready for the migration, we would like to set up Outlook 2016 with our current third-party email company as they currently still manage all of our emails for our company domain.  When we try to set up the email account in Outlook, it appears to recognize the email server because we don't get any error that it connects.  But when we open Outlook 2016, it's not showing any emails.  Are we allowed to set up the Outlook 2016 with got from Office 365 to connect to another email service until we are ready to migrate to Office 365?  If so, is there a process for it?  We're confused why it seems to connect, but then we don't get any emails.  Hopefully I didn't confuse anyone, but please ask any questions you may have.
Christian PalaciosSenior IT Systems AdministratorAsked:
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bbaoIT ConsultantCommented:
> Are we allowed to set up the Outlook 2016 with got from Office 365 to connect to another email service until we are ready to migrate to Office 365?

YES, Outlook application of Office suite technically can support any email provider. technically, it has nothing to do with your O365 business plan.
Mal OsborneAlpha GeekCommented:
Licensing should not be an issue here, you should be fine connecting to a non-Microsoft mail server.

Is the connection to your existing mail server via POP3?

POP3 does not "sync" entire mailboxes like other protocols, it just pulls down a copy of each new inbox item. It CAN then delete the emails it just downloaded which is often default behaviour.

Thus, if another POP3 client downloads a mailbox, it will probably delete those messages from the server. A second mail server will see nothing there to download.

The solution there is to set a time period for POP3 deletion, maybe 2 weeks. In that way, each POP3 client will get a copy, unless the other has downloaded it more than 2 weeks prior.
Vasil Michev (MVP)Commented:
You can use it with any email provider, as long as it supports at least one of the protocols Outlook supports. What you might have run into is Outlook automatically connecting to Office 365, and thus showing you the empty mailbox you have there. This is an unfortunate "feature" that can cause confusion and issues in situations like yours, to work around it you will have to use the reg key detailed in this article to disable the "Check for O365 as Priority" method:

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Christian PalaciosSenior IT Systems AdministratorAuthor Commented:
Thanks Vasil!  This worked as suggested.
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