Gmail w/ MS Exchange server – correct setting for “Leave Messages on Server”

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I am trying to set up Gmail (web application) to work as the client for a Microsoft365 account. (Note: no I don't think this is a particularly good idea, but I am receiving a demand for this function, and if I'm unable to talk people out of their demands then I'd like to have a working solution in hand…)

I know that Gmail should work as a client if the Office365 account has POP3 enabled. (Also this.) I have confirmed that the MS Exchange account does in fact have POP3 enabled. So I was walking through the setup process, but I am stuck at the step where we see the checkbox labeled "Leave a copy of retrieved messages on the server". (Picture credit doteasy.com)

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What would be the most correct way to set this checkbox? If "leave messages on server" is checked, I am worried that I will get duplicates of all received messages. If I do not click this box, then I am worried that the emails will no longer show up on any other clients besides Gmail. At present I can only try this out on a live account where I actually care about the emails on my email server and do not want to corrupt the mailbox.

What is the best way for me to proceed?

Best Answer

If "leave messages on server" is checked, I am worried that I will get duplicates of all received messages.

When Gmail pulls the messages they only get the email that has changed since timeX. They also can see from the message IDs if they already have that message. You shouldn't get any duplicates massages.

Note: if a somebody sends the same message to both email addresses you will get the original message 2 times, and Gmail should make them part of the same conversation.

If I do not click this box, then I am worried that the emails will no longer show up on any other clients besides Gmail.

Exactly. If you don't keep the messages on the server then no other clients can see it.

For example your ISP has email, and you normally use Outlook at home on a PC, and you also want to see your ISP email while you are at work; so you want Gmail to talk to your ISP email. If you don't keep a copy on the server, then anything downloaded by Gmail will never reach Outlook on your home computer, because Gmail told the ISP to delete it.