accessing Maildir locally with Mutt and remotely over IMAP simultaneously

I have Postfix + Maildir + Dovecot + IMAP on my mailserver. I am accessing my mailbox remotely over IMAP with one or more clients (Thunderbird). Additionally, on the server I have mutt configured for local (Maildir) access. When I am connected over IMAP with Thunderbird, and simultaneously start mutt locally on the server, Mutt seems to be confused. When I move a message in Thunderbird (over IMAP), Mutt notices something has changed and reports: Mailbox was externally modified. Flags may be wrong The problem seems to be one-sided. When I manipulate a message in Mutt, Thunderbird registers the change and has no problem with it. **Thus my question:** How can I make remote IMAP client and local Mutt client acccess Maildir without any conflicts/data corruption/errors? **Important:** I am looking for a solution where the Mutt access is local. For reasons beyond this discussion, I don't want Mutt to access the Maildir over IMAP. **Sidenote:** I don't understand why Mutt complains that mailbox was externally modified. After all, Postfix also modifies the mailbox when it delivers new emails.