Email accounts are not showing after migration in cPanel

1. Login destination server, verify the permissions of mail related folders

2. Permission of /home/user/mail  751 and ownership is user.user

You can correct the permission using the command
sudo chown -R user.user /home/user/mail
sudo chmod 751 /home/user/mail/

3. Check the permission of /home/user/etc where it contains passwords of email accounts.
 Permission of /home/user/etc  750 and ownership is user.mail
You can correct the permission using the command
sudo chown -R user.mail /home/user/etc
sudo chmod 750 /home/user/etc

4. You can also correct the mail permission using sudo /scripts/mailperm --verbose username
If the email accounts are still not showing in Cpanel

Check the size of passwd file under /home/user/etc , If it is zero size file, try to copy the files from source server.
If the size of passwd file is zero in source server, then we need to create the mail account with a password manually. Then the password entry will appear under /home/user/etc .

Create mail account with Cpanel script
sudo /scripts/addpop emailaccount passowrd size
sudo /scripts/addpop  test@test.com qwedsa@123 1024

This time, Mail accounts will show in Cpanel for sure. :-)