Hello, I have an iMac--Sierra--Version10.12.1 I have Apple Mail. I am in the process of adding another email account(FASTMAIL). The problem is...

Hello and welcome to ExpertHelp.com! My name is Rofel Lantican and I'm going to do everything in my power to answer your question to your full satisfaction!

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Hi Tim,

Thanks for waiting. Im here to help. Did you get any error message or a notification on the screen before the email address disappear on Apple mail?

Tim,

I can walk you through all the steps to solve your problem. However, we offer a remote support option for $20 where I will perform all the steps for you. It will make the entire process easier and faster.

Will you allow me to remotely access your computer to help you fix your issue?

I understand. Please follow these steps:

1. Open the System Preferences app, and go to Internet Accounts, select + to add a new account.

2. Select to Add Other Account.

3. Select Mail account.
4. Add in your username, your full email address and password.
5. Ensure Mail is selected as an account type.

Then, Add the Mail account on the Apple Mail and let me know if it works. 

Were you able to read my previous post/comment?

If it stays there for more than 5 minutes then it will not disappear from your Apple Mail. The only reason it keeps on disappearing is because it is not added on the Internet Accounts.

Please let me know if you have question. If I were able to assist you on your concern. Please  click the Accept Answer button below and follow the instructions on the next screen.

Thanks

What do you meant create a new mailbox? 

If you will create a new Mailbox on Apple Mail. Mailboxes created in On My Mac are local, meaning you can access them only on your Mac. Your Fastmail already have its own mailbox.

Here are the steps on how to create a new Mailbox.

1. Choose Mailbox > New Mailbox.

2. Click the Location pop-up menu, then choose where to create the mailbox.

   Mailboxes created in On My Mac are local, meaning you can access them only on your Mac. Mailboxes created on your email account’s mail server can be accessed on any computer where you use the account.

3. Type a name for the mailbox, then click OK.

Anything else I can assist you with?

Thanks for your response and apologize for the delay. Will you allow me to remotely access your computer so I can see and check the settings of your computer?

Anything else I can assist you with?