sorry for reviving an old thread, but my question fits here best:
Ive had the same problem as indicated above after a faulty update. /dev/null got replaced by a single file chowned by root.root and 744
After deleting the file and replacing it with a correct character dev everything returned to normal.
My question is: What happened to the mail that was not delivered? Does anyone have insights on this? I ask because locally sent mail would NOT give any error messages as the one suggested in this thread by "external" mailer daemons.
Also: Some mail got delivered (mail to non virtual users afaik) while other mail didn't get delivered. Is it correct to assume that only virtual users were affected or those with specific procmail filter entries?