I was having the same issue with my hotmail account, so I sent a email to HTC asking about the issue - their response is below:
Thank you for your inquiry regarding your Hotmail account on your HTC Rezound device from Verizon Wireless.
AA, I infer that your Hotmail account is a POP3 account on your phone.
The Mail application on our phones originally would keep a copy of all POP3 messages on the phone, even when deleted from the server.
When the devices were first updated to 2.2 firmware, the Mail application was changed to fix this issue, i.e., deleting mail from the server would delete the message from the phone as well.
Many customers did not like how the Mail application was changed, and as a result, the Mail application was changed again to behave as it did originally, i.e., if you delete a message from a POP3 server, the mail will stay on the phone.
This means that users must manually delete messages from the phone, or the messages will remain on the phone as long as the account is set to check mail on the server (default = 3 days).
In addition, POP3 folders on your device do not correspond to the folders for your account, nor do they reflect the account folders. Our native Mail application contains four folders: Inbox, Sent, Draft, and Trash.
If I have not addressed your concern, please include in your response a more detailed description of the issue, and specify whether your account is set up as a POP3 or an IMAP4 account. In addition, please include the IMEI and MEID of your device. To obtain this information, press Home > MENU and then tap Settings > About phone > Phone identity.
We apologize for any inconvenience you may have experienced.
To send a reply to this message or let me know I have successfully answered your question, please log in to our ContactUs site HTC Global ContactUs System - MainLogin using your email address and your ticket number xxxxxxxxxxxxxxxxxxxxxxx.
Let me know if I have successfully answered your question, please click here to complete this.
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Sincerely,
William
HTC
To fix this issue and still be able to use the native email app built into the Rezound, I set-up my hotmail account using the "Microsoft Exchange ActiveSync" option. Now it sync's and works perfectly. You might have to search around to get the settings just right, but it's worth the effort to centralize your emails in one place.
Good Luck!
- AA