Hangup of saving messages when the mail server is not working

If the mail server has changed the connection address, then the messages will be stored forever.
All mail freezes

What you wrote is essentially an unclear statement. Is there a problem you need help with? If so, please clarify. And “mailserver” can mean different things. POP3? IMAP? SMTP?

If the server is unavailable (imap), then all synchronization on other mailboxes will hang.