Help Less frequent/none random reboots?

[Puppa]

I had a couple of reboots when I had one of my mail accounts sync-ing with more than 500 messages. Changed retrieval settings, and haven't had any since. Of course, that may have been coincidence.

 

[LV777]

About once a day. Use to be around 1 a.m., now it has been happening during the day.