change pop account to imap

It would help a lot if you would identify the email service you are using. Not all support both POP and IMAP.

In any event, the POP vs. IMAP server settings will be different. You need to get the settings from your email provider. For example, here are the POP, IMAP & SMTP settings for Outlook.com

Once you know the server settings you will probably need to disable the POP account in Mail and set up a new IMAP account in Mail. And I recommend that you back up your mail folders before you do this.

Something doesn't add up. You should be able to create an account in multiple email clients on multiple computers, smartphones, tablets, etc. all connecting to the same (single) email account on Xfinity (or any other service provider, for that matter). For example, my iPhone & 3 Macs all connect to the same email account that I have on outlook.com (as well as additional accounts on 2 other email providers) and I can see/send/manage my email from all 4 devices.

Here are Comcast's instructions for adding an Xfinity IMAP account to Apple Mail:

https://www.xfinity.com/support/articles/configuring-comcast-email-mac

I hope that helps.

minnron56 wrote:

But I’m not allowed to have a new account because the “account already exists”,

... would be an indication that the account is somehow still on your iMac ... it has nothing to do with the fact that you also have the same email account set up on your MacBook.

Don't touch the MacBook. You have to figure out what's going on on your iMac.

That may be why you are getting the "account already exists" message. I have heard of this issue before and there were different solutions from different users but I don't recall specific details. I'll look into it a bit more and hopefully post some links for you.

The password is not the issue.

I assume you mean that the password you use to sign in to your Xfinity account online is the same as your Xfinity email password, which is as it should be. In Apple Mail (the email app on your iMac) you would of course use the same password when you add your Xfinity email account in Mail.

minnron56 wrote:

change pop account to imap in Mail

You will first have to change the protocol on the email provider's server. Use their webmail login to change your account to IMAP.

Then it must be changed in the email app's Preferences section.

Question - is your Xfinity email address the same as your Apple ID?