IMAP option to not delete from server OR recommend alternate mail app?

Using POP in Windows computer and IMAP on iphone.

In the iphone, POP has the opton to "delete from server: never"

There seems no way to accomplish this in the stock mail app when using IMAP ?

Using POP on the iphone is not an option due to the longstanding issue of the Apple mail apps not sending a proper termination signal back. The mailbox remains locked until the server times it out for inactivity and cleans up the stale lock after 10 minutes. The result is "wrong password" on the computer if it then tries to retrieve during that period. It's a feature of POP by design to use a lock to prevent corruption caused by simultaneous access to the mailbox. BUT, BB,Android,Windows all handle this correctly so that their POP transaction (and the mailbox lock) only lasts seconds! Only ever see this persistent lock with Apple mail clients 😟

The user likes to keep his phone inbox clean, he will delete messages as he deals with them as well as messages he is postponing to deal with on computer later.

Moving messages to a 'later' folder won't help, as that 'later' folder will not be available thru POP (for the computer)

They also don't want to use IMAP on the computer because they don't want their communications stored on the server any longer than necessary.

Can anyone recommend:

- Windows IMAP client which downloads all and keeps a local copy of inbox which does not synch with server inbox.

- Alternate mail app for iphone which allows "delete from device only // never delete from server "