Be sure to check settings at synchronization&storage for the account.

I have checked all the settings.

re : I change the account to imap from pop.

Did you remove the POP account and then create a new existing mail account set up as Imap ? If yes then that's ok.

Do you have any other device which can access the server/webmail account via POP eg: another computer, a phone or even another email client on your computer which you used before and somehow it is running in the background downloading mail without your knowledge ?

I just change the settings for the existing account. Imaps functions are ok except the disappearing emails. I have the account still via POP on a another computor (IMAC) with no disappearing emails. On the phone I use K-9 Mail working together with TB so the emails disappears there as well. I can´t find any setting for the K-9 causes it. No other client is working in the background. I have talked with the provider of the mailserver and they have no such function that should make any email disappear. It´s very strange, they disappear exactly after 7 days.

Retry with 143 but do NOT include password. Wait until account is confirmed and you are prompted later for password. That process has allowed many failed setups to complete successfully.

re :I have the account still via POP on a another computor (IMAC) with no disappearing emails.

The pop account will not see the disappearing emails because there is no synchronising of any folders. Pop account folders are completely independent of server. The emails are stored on the computer in the Pop account. IMAP does not do that. Imap can only show what is on the server. You cannot consider anything in an imap account as a separate independent copy because all imap folders synchronise with the server.

However, the Pop account is capable of popping emails off the server. It is the default for Pop accounts, when you download from server Inbox to pop Inbox, the emails are deleted off the server. This is what the server does unless it is instructed otherwise.

Please check the settings in that Pop account. You must select the option to 'Leave messages on server'.

re: I just change the settings for the existing account.

If you originally set up as Pop and you just changed the settings to try and force a pop account to be using imap server settings then that was a mistake. No where will you find any advise that states to change only the server settings of a pre made POP account to use imap server settings. They do not use same methods. You are forcing a pop account which uses popstate.dat to record what has been downloaded into a imap which uses synchronisation. In the profile Pop and Imap accounts are not even stored in the same location. You may lose emails because the pop Inbox was not set up to synchronise but now is being forced to, so anything previously downloaded and not left on server or subsequently deleted will then get auto deleted. You can end up with all sorts of weirdness because the stored preference settings may end up applying bits of both.

In Account Settings Select 'Server Settings' for the account What does it say top right for 'Server Type:' ?

Menu icon > Help > More Troubleshooting Information Scroll down to 'Mail and News Accounts' section Copy all the information in that area and post it into this forum question.

E-post och diskussionsgruppskonton ID Inkommande server Utgående servrar Namn Anslutningssäkerhet Autentiseringsmetod Namn Anslutningssäkerhet Autentiseringsmetod Standard? account1 (none) Local Folders Ingen Lösenord account3 (pop3) pop.sunhill.nu:110 Ingen Lösenord smtp.sunhill.nu:2525 Ingen Lösenord true account4 (imap) imap.gmail.com:993 SSL/TLS OAuth2 smtp.gmail.com:465 SSL/TLS OAuth2 true account5 (imap) mail.rewire.nu:143 STARTTLS Lösenord mail.rewire.nu:2525 STARTTLS Lösenord true account6 (imap) nmail4.ballou.se:993 SSL/TLS Lösenord nmail4.ballou.se:587 STARTTLS Lösenord true

It´s account6 I have problems with. I have made a change for the POP account in the other computer concerning erasing emails from the server, maybe that will do it?

Problem solved. Sorry to have disturbed you with this issue considering it didn´t actually have to do with Thunderbird. Guess I should have been smart enough by my self to find the solution in the POP account settings in the other computer. Thank you very much anyway!

So what happened? I don't have access to the POP account and only my Thunderbird. Is there a way to retrieve the lost emails and stop this from happeneing?