I use Centos 7.3 with exim builds from the epel repo. Although I
generally try to keep up with new builds, I only check for updates
weekly. I currently am using an exim 4.89 build installed (emergency
basis) from epel-testing, replacing epel build "exim-4.88-3.el7.x86_64".
After only a couple of days running the 4.88-3.el7 build, I accidentally
discovered that it was filling up /var/spool/exim/input with a massive
number of 4K -D files. There were no other files in the spool, only -D.
Lacking -H files, routine checks showed an empty queue.
I have no idea what was causing this, but the issue was resolved by
installing the epel-testing 4.89 build.
Because none of the exim identifiers on the -D files appear in the exim
logs, finding log entries for the missing messages requires matching
file timestamps to log message times. This led to discovery of repeated
disconnects and reconnects from a small number of sources. The massive
number of -D files was due to the massive number of failed retries.
Luckily, it appears that all of the failed messages were from a source
that broadcasts commercial advertising to opt-in mailing lists. It
appears that only some daily alerts on sale items got missed. (My grep
skills are a bit weak, and some of the file timestamps don't precisely
match the log times, so I haven't necessarily tracked down every lost
message.)
