warning: open active ***********: No such file or directory

[Rodolfo González González]

Hello,

a customer is reporting that some of their users tried to send e-mail 
messages using my postfix 2.9.6 server (will be updating soon) but 
messages were not sent. I don't have snapshots of their screens nor 
error messages displayed by their clients yet, but checking the logs I 
find several messages like this one:

Mar  4 12:40:55 email postfix/smtpd[30013]: ***********: 
client=unknown[a.b.c.d], sasl_method=LOGIN, sasl_username=john.smith
Mar  4 12:40:56 email postfix/cleanup[30115]: ***********: 
message-id=<*********.***%john.sm...@example.com>
Mar  4 12:40:56 email postfix/qmgr[21597]: ***********: 
from=<john.sm...@example.com>, size=2509, nrcpt=1 (queue active)
Mar  4 12:59:57 email postfix/smtp[17624]: warning: open active 
***********: No such file or directory

It looks like the queued message is being lost, or it's never written to 
disk, but I have no clue. Any hint is appreciated.

Thank you.