Occasionally an account owner will keep a web archive of all the emails they send to a list. (We do it here at Simplero).
If you want to access a previously sent email and didn't save it, it's simple. (Note: This is only if the list/account owner keeps the web archive. They can deactivate that option)
Go to your account and click on the profile picture and then Your dashboard
Then select Manage email subscriptions
This will open a page showing the lists you are subscribed to. The lists that have the option to see archived emails will show as hyperlinks that you can click on:
If you click on the list, it will show a list of all emails sent to you on that list: