1.In the Mail app on your Mac, select a message from the sender you want to unblock.
2.Move the pointer next to their name in the message header, click the arrow, then choose Unblock Contact.
3.Copy and paste them on your desktop, and delete the original files in the MailData.
4.Check if all fields are filled. If not, fill all the fields with accurate data.
5.If the email is received then it means that your Mail app is the problem, so move on to the next solution.
6.To add an email account using the Mail app, open it and go to Mail > Add Account from the menu bar.
7.Go to Applications to find the Mac Mail app, If it isn’t there, then that’s the reason your app isn’t working.
8.Make sure the one you have on your Mac is the same that your email provider gave you.
9.Click the Spotlight icon in the menu bar, press the Command-Space bar or press the Spotlight key (if available in the row of function keys on the keyboard).
10.Close all the windows you don’t need to minimize the impact on your Mail’s memory.
11.Click the Spotlight icon in the menu bar, press Command-Space bar or press the Spotlight key (if available in the row of function keys on the keyboard).
12.See if the server info corresponds to the one expected. If it does not, you might need to contact your email provider.
13.If the app doesn’t quit, follow these steps to force the app to quit press Option+Command+Esc (Escape) simultaneously.
14.Afterwards enable your accounts one by one. Note: Try not to enable the next account until the one selected before is completely synced.
15.Now select Mail > V7 folder (Depending on your macOS, this could be another number).
16.If it isn’t there, then that’s the reason your Apple Mail is not working. It’s located somewhere else.
17.To quit or close a Mac app normally, choose “Quit” from the app’s menu in the menu bar, or press Command + Q.
18.Select the email account you want to enable emails for, and tick Mail on the right.
19.Go to the Window in the top menu and click on “Connection Doctor.” This will show whether there are problems with connecting to the Mail app.
20.Go to Connection Doctor and check if there are any firewall problems, especially on ports 25, 465, or 587.
21.If there are, again you should contact your email provider and probably reconfigure the server settings.
22.Now re-check account settings and delete and re-add your Mail account to reset this. From there your Mail app folder and every email should be accessible again.
23.Once you’ve located the app with Spotlight, go to it’s folder location simply drag the Mac Mail app icon to your Applications folder to relocate it.
24.Take all accounts online: Click the lightning bolt icon or choose Mailbox > Take All Accounts Online.
25.Under Account Information, make sure that the account is turned on and the status is online.
26.Find this folder: Containers > com.apple.Mail > Data > Library > Saved Application StateDelete saved Mail states.
27.Open the Terminal (Applications / Utilities or you can use Spotlight to open the Terminal app).
28.Check to see what filters you have turned on as Mac only allows filters applied only in the current Mail window.
29.You can even force the Finder to quit, if it stops responding: Select Finder in the Force Quit window, then click Relaunch.
30.Take a specific account online (if you have more than one account): Click the lightning bolt icon next to the account’s mailbox, or choose Mailbox > Online Status > Take [account] Online.
31.Check if your Mail is in the right place – the Applications folder. You want to make sure the version of the Mail app you’re trying to open is located in the Applications folder.