Please understand that block capitals are read as shouting.

Look under Tools|Account Settings|{select account}|Synchronization & Storage for settings about message deletion and retention in IMAP-connected accounts.

In POP-connected accounts and Local Folders there are similar settings under the heading Disk Space.

It's possible that your email provider has an automatic deletion policy too, though I think this would only be relevant with an IMAP-connected account. If you are not able to adjust this setting, you may have to move messages into Local Folders.

I have checked under synchronization and storage and they are already set to "do not delete". Is there any other place that I can check? I appreciate you taking time to help me.

Are you using any other devices or programs to access this account? Any possibility that any of those could be deleting messages?

I'd also check with the email provider/ISP to see if they have a specific policy on deletion of "old" messages. And check if any of these lost messages can be found via their webmail site.

Do have a look in your Trash/Deleted/Bin folder for deleted messages.

I checked with my ISP and they said they just recently started deleting messages over 30 days old. They were no help to me. I checked my trash folder and it is "also" being deleted after 30 days. I would just like to find a way to keep my messages until I delete them. Is there any other place that I can see if something has been checked and is deleting my messages? I am not using any other devices or programs to access the account. I can't help but think that something has been changed on my TB account because I was not having this problem until a few days ago. Thank you for helping me.

Let's see, your ISP admits they delete after 30 days and you are still looking for a box to check in Thunderbird. ???

Make Folders under the Thunderbird Local Folders account and move the messages you want to keep there. Local Folders is on your local drive and out of reach of your provider.

You, of course, appear to make fun of me and embarrassing me here but I honestly don't think it is your place to embarrass me. Who do you think you are to make fun of someone who doesn't know as much as you think you do? I stated at the beginning of my query that I was an older person and was not well versed with computer problems. I do not do much on the computer and when I saw my emails were deleted all of a sudden I asked for help. Maybe TB does not like to be friendly with people with questions. I do not understand the fact that my ISP has just started deleting emails over 30 days why that would make it happen in my email program that are removed from their site daily. I don't know if you work with TB or are just a subscriber like me. Either way I am very frustrated with my problem as well as being frustrated with the way you treat another subscriber. Now I am stuck with my original problem of having my emails deleted over 30 days old and appear to have moved backward instead of forward.

You must be using IMAP. This means that your messages are stored on the server, and Thunderbird is acting as a remote viewer. If you do something in Thunderbird, such as move a message from one folder to another, then that action is repeated on the server.

So, any changes made on the server are also shown in Thunderbird. This is an advantage for users who see their email on several different devices, such as their computers at work and at home and also on a phone. If a message is deleted, it disappears on all of those devices. You don't need to delete it separately on each one.

In your case, because of this unhelpful decision to delete your messages for you, you need to move your messages to somewhere out of reach of the server. As Airmail said, you must move your messages to the Local Folders account in Thunderbird. It is a clumsy solution but you are faced with a rather silly policy that has been put in place by your email provider. I think it is rather wicked of them to have introduced this change without warning you. Maybe they did but not in such a way for you to be able to grasp the consequences. Businesses generally try to downplay any change that reduces the quality of service.

Another approach would be to change to a different provider who operates in a more rational way, but then you have the upheaval of changing to a different email address.

Yet another approach would be to set this account up again using POP, where Thunderbird would just collect messages from the server, store them locally and instruct the server to delete them.

And do complain to your email provider. They should be made to understand that deleting your messages for you, without your express acknowledgement of this change in policy, is unacceptable. It seems to me that they have failed to procure sufficient storage to be able to offer their clients an up to date IMAP email service, and they expect you to tolerate the outdatedand simplistic POP service. That is simply not good enough in an era where many users will wish to use multiple devices.

I spoke to the head of the department at my ISP as you suggested to complain about deleted messages and he assured me that they "do not" delete messages. He said I was misinformed by the person that took my call and told me they did. He said they never delete. He said it was their job to store my information. So now I am back to something that is in Thunderbird taking my messages off. This is happening in my inbox as well as my trash folder. My ISP is assuring me that they do "NOT" delete. So now I am in a position where I am told by the head of my ISP that there would be no reason for TB to delete my messages since I have had the box checked that says "do not delete my messages" Could something be wrong on TB's end that possibly I have not configured something correctly?

Do you have just the one account? These settings must be attended to for each account, and you will have at least two; your email account proper and Local Folders.

In Local Folders it is under Disc Space. Given that we think your working account uses IMAP, it would be under Synchronization & Storage. You need to check both of these locations.

I looked under disc space and synchronization and storage and both areas say not to delete any messages. How can I create a new folder in the local folders area and send old messages to it? How can I use the archive folder and make old messages go to it?