I have an mqueue full of files ending in X but I can't work out why they have an 'X', what an 'X' means, and why sendmail wont process them (googling adding 'X' is too vague it would seem :)
e.g.
/var/spool/mqueue (70 requests)
-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------
t9QM56ql012231X 99091 Tue Oct 27 09:05 <...
t9R7dTje012912X 97292 Tue Oct 27 18:39 <...
.
.
A sample qft9QM56ql012231 start:
V8
T1445897106
K0
N0
P129683
Fbs
$_[192.168.0.46]
$rESMTP
$suserPC
${daemon_flags}
${if_addr}192.168.0.240
S<...
rRFC822; ...
RPFD:<...
H?P?Return-Path: <�g>
(I've replaced all email addresses with '...' of course)
man mailq
DESCRIPTION
Mailq prints a summary of the mail messages queued for future delivery.The first line printed for each message shows the internal identifier used on this host for the message with a possible status character, the size of the message in bytes, the date and time the message was accepted into the queue, and the envelope sender of the message. The second line shows the error message that caused this message to be retained in the queue; it will not be present if the message is being processed for the first time. The status characters are either * to indicate the job is being processed; X to indicate that the load is too high to process the job; and - to indicate that the job is too young to process. The following lines show message recipients, one per line.
You can use uptime come to get system's load averages.