I have the problem (I think since Mountain Lion) that some mails fail to import with the following error:
09:12:10: Error importing message “xxxxxxxx” from “xxxxx” at 2012-08-10 15:15:06 +0200 [NOTE: this exception originated in the server.]
*** -[NSProxy methodSignatureForSelector:] called!
it happens with different IMAP servers
with The Mail Importer and also when I try to add only one of the messages via “Message/Add to DevonThink” in Mail.
the amount of failed imports is for example “29 out of 229” or “121 out of 1137”
Might be an IMAP sync error on your Mail client. Try this: in Mail control-click a mailbox and select "Synchronize ", then wait for the Mail client to sync with your mail server, and re-try the import. Depending upon the mail server, connections, and cussedness of Apple Mail , it can take a good while to re-sync with IMAP.