perhaps explain exactly what you did to mess things up, then someone might have a clue how to undo that.

Thank you for your interest, Matt! The following is exactly what happened: I have two Thunderbird pop email accounts with the same email provider, on my Apple iMac. Both accounts have been active since 2011. The email provider recently required making some account changes, to improve security. Because I hadn't received a message about that, I contacted the provider support system. The support person advised me to do a specific process, and then walked me step-by-step through that process that involved 1) having their system generate a new account password, 2) then removing my account, and 3) then reopening my account, using the new password. I was very concerned that removing the account would cause loss of emails, but the the support person told me they would NOT be lost. Further, when I expressed deep concern, she strongly stated that that would not happen, and that she had helped several others go through this process with no such problem. I then agreed to move forward with the process, and when it was over, I had lost all but a very few recent messages in my inbox and sent "box". The support person first had me wait a few minutes and then tried several things and finally did not know what to do. On checking, I realized that she probably thought that I had an imap account and/or did not realize that messages would be lost with a pop account. I recontacted the email provider support department, and discussed this with another support person. After about a half hour, he said there was nothing that they could do and that they did not have any info about Thunderbird or using Apple's Time Machine. I have an Apple 2021 M1 iMac with OS 11.4. PLEASE NOTE: I am not an IT expert nor have had any IT or computer training, I am only a reasonably intelligent person. I hope this information is what you need.