When a Google apps user is no longer are needed, you may want to delete the account and transfer all data and emails under another user . For this exercise we will assume the deleted user emails are migrated to the admin email account.
To ensure no emails are lost from the deleted user, first create a label and filter under the admin gmail account with the email name of the user
Now log into the user gmail account and click My Account > click Sign-In & security
Scroll down to the Allow less secure apps: ON click to turn it on
Log back into the user gmail and go to settings by clicking the gear icon > Forwarding and POP/IMAP
Under POP Download click Enable POP for all mail (even mail that’s already been downloaded) and Save Changes
Now log back into the admin gmail and go to settings >Accounts
Under Check mail from other accounts (using POP3) click Add a POP3 mail account you own
In the next popup window enter the email address of the user and click Next Step
Enter username (gmail address) and password
POP Server: pop.gmail.com Port: 995
Tick the boxes: Always use a secure connection (SSL) when retrieving mail
Label incoming messages: (select the correct label to migrate under)
Archive incoming messages (Skip the Inbox)
click Add Account
Next window select No. The below video demonstrate the entire process.