I think a recent change tried to send output from crontab to dev/null to avoid messages appearing a) when setting the crontab, b) whenever mailsync is run.  However the redirection was for the string concatenation meaning a null string was piped to cron obliterating the crontab (thank goodness for backups). I have put the redirection in the correct location (similar to a few lines above when removing the mailsync line).  I have also redirected all output of the mailsync (both errors and normal messages) to dev null.