found another interesting field of the process list to watch,
"start time". Tells you how long k9mail survived without
a crash - and makes it much easier to search the logs to figure
out what happened around that time.
On my systems both k9mail versions mostly work for around an
hour even when not in use, somehow restart after that. The device
show 25MB of free RAM when k9mail runs.. must be some unusual
memory spike.
Adding memory pressure makes k9mail crash much earlier.