A\"‡" [imap-enable-exchange-bug-workaround data x buffer uids props string-match "The specified message set is invalid" make-local-variable t imap-fetch signal receive nouidfetch] 6)
  imap-fetch-safe(("*" "*:*") "UID")
  imap-message-appenduid-1("misc")
  imap-message-append("misc" #<buffer  *acc*> nil nil " *nnimap* mail.shopzillainc.com")
  nnimap-request-accept-article("misc" "mail.shopzillainc.com" t)
  gnus-request-accept-article("misc" (nnimap "mail.shopzillainc.com" (nnimap-address "mail.shopzillainc.com") (nnimap-stream ssl)) t t)
  gnus-inews-do-gcc()
  run-hooks(message-sent-hook)
  message-send(nil)
  message-send-and-exit(nil)
  call-interactively(message-send-and-exit)

The *imap-log* buffer shows

[...]
68878 OK APPEND completed.
68879 EXAMINE "misc"
* 154 EXISTS
* 1 RECENT
* FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)
* OK [PERMANENTFLAGS ()] Permanent flags
* OK [UNSEEN 125] Is the first unseen message
* OK [UIDVALIDITY 156] UIDVALIDITY value
* OK [UIDNEXT 3039] The next unique identifier value
68879 OK [READ-ONLY] EXAMINE completed.
68880 NOOP
68880 OK NOOP completed.
68881 SELECT "info"
* 37 EXISTS
* 37 RECENT
* FLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)
* OK [PERMANENTFLAGS (\Seen \Answered \Flagged \Deleted \Draft $MDNSent)] Permanent flags
* OK [UNSEEN 36] Is the first unseen message
* OK [UIDVALIDITY 148] UIDVALIDITY value
* OK [UIDNEXT 38] The next unique identifier value
68881 OK [READ-WRITE] SELECT completed.
68882 STATUS "info" (UNSEEN)
* STATUS info (UNSEEN 2) 
68882 OK STATUS completed.
68883 EXPUNGE
68883 OK EXPUNGE completed.


I suppose the backtrace happens when it stores the Gcc: copy.  The copy
makes it into the group just fine, and the email gets sent to all the
recipients.  If I send without Gcc:, I don't get the backtrace.

Any pointers would be welcome.

Thanks,

Bjorn.