Please explain further what you mean that your "email format has changed". The padlock on the envelope icon does not mean your email account is locked, but that it uses an encrypted connection to receive/send messages.

We cannot now get past emails, folders or tagged emails.

How do we retrieve our past emails, folders and tagged emails please?

How can we unlock the keypad?

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"Unlock the keypad"? What's not working? Which keypad? How is it "locked"?

Thank you for responding. tjohnson expained that the padlock meant there was an encrypted connection in place. We do npot understand what effect this has on us. We would just like our back copies if sent and received emails returnes. At the moment we just have records back to the 26th May when the rest were lost.

It is your copy of Thunderbird software on your computer. There is nothing anyone here can do to change the state of things. You have to do that.

We can offer suggestions based on information you supply but that is all.

So far you have not actually provided any more information that "it does not work how I think it should" so you have people guessing.

Missing historical mail could have a load of causes. Not the least being your anti virus ate them (Seriously).

Your secure connection is a fact. it is not relevant at all unless you have been changing account settings. They do not change by themselves and therefore you have had a secure encrypted connection all the time you have had Thunderbird.