How can I retain the re-writted mail from thunder bird

Question

Recently our mail server changed to Office 365 from Mithy server. Unfortunately when our It team changing the setting, my inbox got re-writted and I lost all old mails. Kindly let me know, if there is any possibilities to retain those deleted mails....
Thanks.
Abhilash A A

Answer 1

Your IT team should have advised you that changing to another server would not give you access to any emails held on the old server, assuming you were using IMAP.
This would have afforded you time to get emails off the old server.
When the server changed, you would have needed to alter the server settings and that meant you were looking at a different server.
It would not be unreasonable to assume that the IT team should have migrated all the data/emails so that when you change the settings you can still see all the folders and emails. Clearly this did not occur.
Maybe the server is still accessible but you would have to create a new imap mail account and connect to the old server settings.
If this works, then synchronize all folders for offline use to keep a copy on your computer.
see: https://support.mozilla.org/en-US/kb/imap-synchronization#w_configuring-synchronization-and-disk-space-usage
Then in offline mode, move those emails into Local Folders.
If you cannot setup a mail account to access old server then chat to the IT department and ask them how you access/download etc old server in order to move your emails. They are the only people who can access servers.
If you ever get personal emails sent to business email address then move them into Local Folders, then you can back them up, save as .eml files etc. But they will be on your computer and not affected by a server change.