iPhone doesn't delete email off Yahoo server

Under Settings --> Mail, Contacts, Calendars --> Accounts (yahoo account) --> Advanced --> Mailbox Behaviors --> Deleted Mailbox, make sure On the Server, Trash is selected.

That USED to be the case, but now under Advanced, I have On My iPhone with Trash selected, and under Server, there is NOTHING! All emails stay on my server. How do we go about getting a fix in the next update? (All my software is up to date, on phone and on pc)

kj38, i believe yahoo email is usually set up for POP forwarding meaning when you sync emails from yahoo email to a client (eg, iphone or outlook), emails are pulled from the yahoo server but when you delete them that info is not communicated back to the yahoo server. Gmail is set up on IMAP which allows that two-way communication.
But I believe for the iphone, yahoo email does sync via IMAP, you just have to fiddle with the advance settings on your iphone to make sure emails are deleted. Under Settings --> Mail, Contacts, Calendars --> Accounts (yahoo account) --> Advanced --> Mailbox Behaviors --> Deleted Mailbox, make sure On the Server, Trash is selected. When you delete emails on your iphone, it will now send them to the "Trash" folder on the yahoo server instead of the iphone (ie, moving the email from the server & iphone inbox to the yahoo server trash box.

Either way, neither gmail nor yahoo will allow true syncing of your email, calendar, and contacts across iphone, email server, and a PC/Mac unless you have an Exchange server account or MobileMe. I just understood this myself and am now considering getting mobileMe. For example, even with the setting described above, if you were to go to your yahoo or gmail account and then delete emails on the online version after having iphone pull them, it would not delete the email on the iphone. That type of true syncing, I believe, requires Exchange or MobileMe.

Ah-ha

In Settings > Mail, Contacts, Calendars > Accounts (my account I'm working on), I tapped the Account, turning it off, then back on. Took a little while for this account to become active again, but when it did, the Advanced > Deleted Mailbox > On the Server options reappeared. Yes!

Now I have selected the Deleted Messages for On the Server.

I sent a message from a different account to this account in question, I received it on iphone, I deleted, and it went to trash on my phone.

I logged into the server, and alas, I see the message in my inbox. I want it to be deleted off my server. How do I do that?