permanently deleting emails

Hi
I have a macbook pro and an iPhone 6S. I have deleted and permanently deleted emails on my phone and computer which I no longer want or need and have about 200 emails in my Mac Mail inbox. I have also set my computer and phone to permanently delete emails after one week on my phone and one month on my computer in all my email accounts. In one of mail email accounts they are making some changes (Bell Simpatico) and consequently there is an account thru Microsoft to view all my emails. The problem is there is the usual inbox, sent, deleted etc but also a POP column that lists approx 24,000 emails. These emails are from all my email accounts, iCloud, Outlook and Sympatico (Bell Canada) and looking thru this there is every single email I ever received since the beginning of about 2012 (which I'm guessing is when the cloud started). i am currently going thru and deleting most of them. I don't know that it is possible to delete the whole bunch without deleting the few emails that I'd like to keep. The inbox only contains the last 20 or so emails. I was rather surprised and disheartened to find all these still exist. Is there any way to permanently delete emails?
Much thanks for any help.

There's a fair bit to wade through but the biggest issue you have is that one or more of your email accounts are POP accounts.

Stop me if you've heard this one...... domestic email comes in two main forms IMAP and POP. Without delving too deeply the big difference is that POP accounts do not pass changes back to the email server.

e.g. if you get an email delivered from a POP account to your Mail client on your Mac/PC/mobile device etc it's just a copy of the one that's on the email server. You can delete it on your Mac, empty the trash, securely erase the hard drive and bury it in the garden for 5 years. None of that will change the fact that there is still a copy on the mail server.
So the next time you connect you can get that mail delivered all over again.

Some POP accounts allow you to log in online and change the settings to delete the server copy once a client requestes a copy but not all support this. Ideally, you're best using an IMAP capable service. IMAP accounts cascade changes. I.e. you delete on one device and it's deleted everywhere.

Thanks for replying

So bottom line is I'd have to get rid of my Simpatico account. Ok good to know.
Thanks