Anybody able to help with this topic please ?

Anybody able to help with this topic please ?

Any chance that this is a gmail account and the folder is allmail?

Is your account an institutional (work, school, etc.) account?

No its not a gmail account work contains multiple e-mails but the e-mails in question are in one particular folder

ALSO

When I open a folder and go straight to "inbox" the inbox folder does not open i have to go open another folder first and then come back to inbox and then it will open - this happens across all accounts.

work contains multiple e-mails but the e-mails in question are in one particular folder.

It's hard to know what you mean because "email" now means three different things (account, address, message). You may be using it to mean different things in this one sentence. And you seem to use "folder" to mean "account" sometimes? Otherwise I don't know what it means to open a folder and go straight to the inbox.

So you have multiple accounts (identified by different e-mail addresses)? Is the account in question an institutional (work, school, etc.) account, i.e., one administered by a school, employer, or other organization?

Institutions put warnings about external mail in headers. Is your institution doing that?

The re-appearing messages always have an external mail warning?

Are you using anti-virus software?

when I open an account and click on the inbox (folder) the inbox does not open - until i click on and open another folder in the account - i can then go back and click on inbox(folder) and it will open (showing all of the messages)

The accounts vary as to who administers them some g-mail but most administered from a small company that looks after private company e-mail accounts. The warnings don't appear to come from the service provider (I will check with them!)

Re appearing messages i think all have warning embeded within them !

Anti-virus on laptop is simply Avast

I would do two things:

1. Start Windows in safe mode with networking and see if the problems persist. Anti-virus software can cause many issues in Thunderbird.
2. If that doesn't identify the cause, ask your administrators about what they are doing that might prevent you from deleting and moving messages on which they have put a warning.