I have just unregistered a domain. Now my mail client (Thunderbird) popped up a message saying that it cannot connect to the mail server. That's fine - for the moment.

However, I wonder what would happen when someone else registers the domain. Given the registrar would have an interest in attacking, would it be possible for him to figure out user name and password from a dangling client that repeatedly tries to connect?

Obviously, people would not immediately delete their mailbox locally. Perhaps there are still some mails to be archived or similar.

Is there some kind of "last action" a mail server can send to the client in order to prevent the mail client from connecting to a future server on the same name?

For my mailclient, Thunderbird does not have an option for disabling an account. I can also not delete the server name completely. It wants a valid server name. If nothing is entered, it will automatically choose the old name again.

I have just unregistered a domain. Now my mail client (Thunderbird) popped up a message saying that it cannot connect to the mail server. That's fine - for the moment.

However, I wonder what would happen when someone else registers the domain. Given the registrant would have an interest in attacking, would it be possible for him to figure out user name and password from a dangling client that repeatedly tries to connect?

Obviously, people would not immediately delete their mailbox locally. Perhaps there are still some mails to be archived or similar.

Is there some kind of "last action" a mail server can send to the client in order to prevent the mail client from connecting to a future server on the same name?

For my mailclient, Thunderbird does not have an option for disabling an account. I can also not delete the server name completely. It wants a valid server name. If nothing is entered, it will automatically choose the old name again.