Hello Homer777,
Thanks for posting in Apple Support Communities. We're glad you're here.
We understand that you'd like to personalize your Mail settings for the iCloud email address to delete any emails after a specified interval. We'll be glad to direct you to the setting where you can make this change.
Open this link to view the options to Delete and recover emails in Mail on iPhone, then scroll down to the section entitled "Decide how long to keep deleted emails" where you'll find these steps:
"You can set how long deleted emails stay in the Trash mailbox.
- Go to Settings
> Passwords & Accounts. - Tap your email account, tap Mail (below Advanced), then tap Advanced.
- In the Advanced settings, tap Remove, then select a time interval.
Note: Some email services might override your selection; for example, iCloud doesn’t keep deleted emails longer than 30 days, even if you select Never."
We trust this does the trick.
Best regards.