The environment variable PSA_SYN_FRC_CHK_IN lets you force external emails to be checked in if the system erroneously considers them as having been checked in already.
Values:
- n = Emails are identified by their GID and are not checked in once again.
- ask = Emails are identified by their GID, and you can decide whether they should be checked in once again.
- y = Emails are identified by their GID and are checked in once again without query.