I have a recently changed my password on my btinternet account and and no longer able to access incoming mail on my imac. It all works fine on my iphone. Any thoughts?

I understand from your post that your e-mail account on your Mac will no longer receive but it can send. If this is correct then please follow the directions below to first remove and then add your account.

When you remove an email account from Mail, the account’s messages are deleted and no longer available on your Mac. Copies of messages remain on the account’s mail server and are still available (from webmail, for example).

Important: If you’re unsure whether messages you want to keep are still on the mail server, move or copy them to a mailbox stored on your Mac (the mailbox appears in the On My Mac section in the Mail sidebar) before you delete the account in Mail.

1. Choose Mail > Preferences, then click Accounts.

2. Select an account, then click the Remove button .

   Note: If the account is used by other apps on your Mac, you’re asked to remove the account in Internet Accounts System Preferences. Click the button to open Internet Accounts, then deselect the Mail checkbox for the account. To stop using the account in all apps, make sure the account is selected, then click the Remove button .

Then follow these steps to add it back:

• The first time you open Mail, it may prompt you to add an email account (if you haven’t yet done so). Select an account type, then enter your account information.

  If you don’t see your account type, select Other Mail Account.

• To add another account, choose Mail > Add Account, select an account type, then enter your account information. Make sure the Mail checkbox is selected for the account.

• If you already use an account on your Mac with other apps, such as Contacts or Messages, you can also use the account with Mail. Choose Mail > Accounts to open Internet Accounts preferences, select the account on the left, then select the Mail checkbox on the right.

Take care.