My ISP is working to resolve a problem with a mailbox in my account. Its a critical mailbox so I set up a Hover email mailbox account for the same address and changed the DNS MX record accordingly. I also renamed the TB account configurations for the ISP mailbox and set up new TB accounts for the Hover mailbox.

Sending and receiving for this mailbox both work properly with this one exception: if I use Thunderbird to send a message to myself from another TB account the message still goes to the old ISP mailbox. It is as if TB is ignoring the DNS and using a stored MX address. The address of this moved mailbox has been removed from the address book in case old server information was being held there but problem behavior persists. Any ideas on where the old server address might be stored and how I might delete it? Thanks.