If you never want any messages deleted off the server then in 'Server Settings':

• select 'Leave messages on server'

This would mean you would have to manually access your webmail account via a browser to remove any old emails. Please note: Pop servers have a quota of stored space. If it gets full then the server will not be able to receive any emails sent to it until you make space by deleting old emails.

If you want to leave messages on server but only for a limited time then in 'Server Settings'

• Select 'Leave message on server'
• Select 'For at most eg: 1000 days'

Note: when you compact the pop eg: Inbox' to remove all old traces of deleted and moved emails, then the emails older than 1000 days should get removed off server.

But this 'older than 1000 days' has no effect on the Pop account because it does not synchronise with server - only imap accounts synchronise with server. Meaning, unless you have deleted them from the pop account then they will still be visible in the pop account.

New Pop accounts will download whatever is in the server 'Inbox' because the new 'popstate.dat' file; which keeps a record of what it downloads so it does not keep redownloading everything; has no previous record of downloads, so it fetches everything from server Inbox. Dates are irrelevant.

All Pop accounts download and store emails on your computer which means they can be copied from one computer to another. If you copy the entire account it will include the 'popstate.dat' file, so once you have created a new pop account and set it up to point to the copied in account then it will use it. In which case, only emails that are recent and not previously downloaded will get downloaded.

If you never want any messages deleted off the server then in 'Server Settings':

• select 'Leave messages on server'

Note: when you compact the pop eg: Inbox' to remove all old traces of deleted and moved emails, then the emails older than 1000 days should get removed off server. But this 'older than 1000 days' has no effect on the Pop account because it does not synchronise with server - only imap accounts synchronise with server. Meaning, unless you have deleted them from the pop account then they will still be visible in the pop account.

Thanks; this is eye opening to me. I have a few questions about the quoted portion of our post: I'm not sure what you mean by "Compact the POP". I'm guessing you're referring to the server (webmail) and not the Thunderbird inbox, but I don't know what compact means.

The biggest comment has to do with your remark about the 'older than xxxx days' being irrelevant on POP accounts. I am not disputing this, but is this documented somewhere? I would actually hope that when I chose this option for a POP account I should get a warning message.

Last but not least: I want to make absolutely sure I understand the distinction between your use of "POP account" vs. POP server. Are you saying that the 'older than xxxx days' option refers to deleting emails from the Thunderbird email account and not from the POP server? That seems strange since this is an option under "Leave messages on server " This is crucial. I have always been under the impression that deleting emails from the Thunderbird client was something explicit, i.e. the user had to select/mark one or more emails and then manually delete them.

If this is what you are saying, then there are only 2 ways to delete emails from a POP server: 1. Manually delete them from the server using a browser and the webmail server. 2. Delete them from Thunderbird and have the 'until I delete them' option delete them from the server the next time I download new emails. This is completely counterintuitive.

Sorry to hammer these points, but I must be sure I understand what you're saying. This is especially aggravating since in another question I asked a while back, I was told by another contributor that my method of manually deleting emails from the server was inefficient, and told me to use the 'older than xxxx days' option! Hopefully you can see how frustrating this is.

re :"Compact the POP"

Do not confuse 'Compacting' with 'Compressing' they are not the same process.

This 'compacting' process is done in Thunderbird.

Thunderbird downloads emails and stores them in an mbox file called 'Inbox' with no extension. The mbox file is a text document and emails get appended to it one written after the other.

When you move or delete emails from the Inbox, they will display in the relevant folder. The email in Inbox gets a special tag applied so it is marked as deleted from Inbox and is therefore hidden from view. However, that original email is still in the Inbox mbox file.

When you compact the pop Inbox folder, a process commences which checks through all the contents of that 'Inbox' mbox file looking for all the good wanted emails and copies them to a new file - it ignores all the emails that are 'marked as deleted'. Then the new Inbox file replaces the old one. This cleans up the Inbox mbox file thus reducing space and is a vitial part of housekeeping to maintain a healthy file. This 'compacting' process helps to reduce risk on getting a corrupted file.

To explain this in a more visual manner - imagine you have one single text document and imagine each paragraph represents an email. Paragraphs you do not want get a big red strike through, so over time it starts to look messy and harder to read. So you clean up the text document by removing all those paragraphs with a red strike through and resave the file. Now it uses less space, is a smaller document and easier to read.

To compact the Inbox:

• Right click on pop account folder called 'Inbox' and select 'compact'.

The folders that need the most 'compacting' tend to be Inbox, Drafts and Junk because they get the most activity when it comes to moving emails or deleting emails.

More info on compacting:

• https://support.mozilla.org/en-US/kb/compacting-folders
• https://kb.mozillazine.org/Compacting_folders

Advise: Do not use folders that are inthe process of being compacted. The process is quite quick merely seconds. Do not exit Thunderbird whilst compacting is occuring.

Toad, thanks for your excellent answer to my question about compacting. However, you didn't answer my second question regarding the 'older than xxxx days' setting under Leave messages on server. I'm pretty sure that I now understand that this setting has no effect on the contents of the email server at my ISP, which was a big surprise to me. But I'm still very concerned as to what (if any) effect it has on the contents of my Thunderbird email account. Part of your original response made it sound like that setting would delete emails older than 1000 days from Thunderbird. That is not what I want. The only time I want emails deleted from Thunderbird is when I explicitly mark and delete them. Please clear this up

I did some searches in Thunderbird and did not see any evidence that emails older than 1000 days had been deleted but I really need to have to definitively answer this. I have unchecked the 'older than 1000 days' box in order to prevent any future damage but I need to understand exactly what that setting did or didn't do.