Hello,
That's right. Like the POP3 spec says:
today it happened again. I was out of office for several days and now I had to download >3.500 messages at once. dovecot pop3 struggled after downloading about 1000 messages or so. I started downloading again. Some error again after about 1000 messages. I removed all dovecot-files from the Maildir. It happened again. This must be an error in dovecot. So I switched back the pop3 service to qmail-pop3d now, while imap is still running through dovecot. With qmail, the error didn't happen. The dovecot-response "Message is deleted" is not correct and does NOT result in downloading a deleted message. I checked with qmail:
retr 7 <message-data> . dele 7 +OK retr 7 -ERR already deleted
So if it really would be a problem of Mozilla Mail, it would have occured with qmail anyway.
Regards Marten