Sry that’s happened. eM Client does warn you before you actually removing the account and also tells you it will “delete all folders” for a POP or IMAP account as in the example screenshot below.
If you have a POP account without an eM Client backup, if you have done a recent eg: computer image backup of your entire computer, you could restore that to bring back your emails. The only other option, would be if your ISP or Mailbox providor keeps eg: daily mailbox backups they may be able to restore your mailbox. Contact your mailbox support. Some business isp providors do offer that.
If you have an IMAP, Exchange or iCloud account, just re-add your account and your emails will automatically come back from your mail server.
Suggest for futue to setup automatic eM Client “daily backups” via “Menu / Settings/ General / Backup”. Or at least do regular manual backups via “Menu / Backup”.
(How POP mail works).
If you have a POP account (using any email client) normally your emails are automatically deleted in the email client when you remove an account as they are (attached to the account locally). POP mail by default downloads mail from the server and then deletes all the emails from the server, so you only keep emails locally. This is generally done so you don’t take up alot of space on your mail server as most ISPs or Mailbox providors only give you limited mailbox space unless you pay extra.
Before removing a POP account you normally create a folder called eg: “Old Mail” down in (Local Folders) at the bottom left in em Client and then drag your current POP mail folders down to that folder intact so emails are then not deleted when you remove & re-add the POP account. Then once you have resetup your POP account again, you drag back up all your Old mail to your new POP account.
(How IMAP mail works)
If you have an IMAP , Exchange or iCloud account, you can remove & re-add accounts as you are merely “just reading email headers remotely” from your cloud mailbox. So the emails are not all automatically downloaded locally to your mail client when you receive mail and also (not automatically being deleted from the mail server) after downloading your email.