When I delete an email from my iphone it also deletes it from the server, how can I keep on server

You sent up your email account as a imap account - which is why it deletes from the server.

You will need to set it up as a POP3 account, if possible, then your email will stay on the server.

In Advanced section of your account on the Phone there should be another section further down labeled. Delete From Server under Incoming Settings.

If you set that to never, the emails will not be removed from the server.

Ok, you're welcome.

Have you confirmed that with your IT dept?

Is this an exchange account?

If the account is IMAP based all you can do is set the deleted emails to the Archive Mailbox And set the Remove option to Never.

IMAP accounts unlike POP accounts (which Yahoo uses) will sync changes across devices. So if you delete an email it will be deleted at the server.

Archive instead to keep them on the server for later review.