If you were deleting mail then they typically go to the 'Trash' folder. You could access the Trash folder and move them back.

Do not compact anything. If you have auto compacting enabled then switch it off.

• Settings > General
• scroll to 'Network & Disk Space'
• uncheck - 'compact all folders when it will save....'

Is this an imap account or a pop account or emails stored in 'Local Folders' account?

How exactly were you performing the delete? Select email to open and click on 'Delete' button Right click on email and clickon the top right bin delete message icon? Did you enable the 'Delete' column header and you were clicking on relevant bin icon? Or did you highlight emails to see 'X' number of conversations and then click on 'Delete' button OR did you set up a Retention Policy for a folder which says delete messages more than x days old ? There are more ways of deleting - but what did you do exactly because it sounds like you have highlighted/selected a lot of emails.

If you were using the keyboard and pressed 'del'....is it possible you have a sticky key and it kept sending a delete instruction to the computer which in turn did as it was instructed in said program. Basically, as the email you wanted to delete got erased, focus is put on next message, but what if that 'Del' key was still slightly depressed......! Check your keyboard if that is the case, to prevent another incident.

Report on whether emails were in trash; method of deleting, inform us if compacting has occured anyway, what type of mail account imap or pop, if pop are emails still on server ?

I have an imap account. I unchecked 'compact all folders when it will save..' When I was deleting a mail I selected it and then clicked on the delete button my usual method, very seldom do I delete more than one at a time. The deleted mails go to the Bin folder rather than the Trash folder which is empty. The mails that are missing are not in the BIN folder. Prior to this event Thunderbird was flickering a lot particularly the folders I had to shut it down using task manger before I could use it. Another event happened last week when I clicked on new message the window opened continuously and would not stop, again I had to use the task manager to shut it down. At all times I was using a wireless mouse. I am not sure how to know if compacting has accured.