I gave Evolution a try but I didn't like it so I uninstalled it and purged it using terminal. or so I thought. It was still showing in "installed software", so I uninstalled it there too.
I went into Google settings and removed it from there too, and double checked just now - it's gone - because I keep getting this pop-up every few minutes and it's driving me mad!
Get a list of installed packages first, and filter by name:
apt list --installed | grep evolution
See what that comes back with, so you can then remove it.
Alternatively, since it's clearly running in the background, you can check active processes to see whatever remnants are still in place — did you try to restart already?
pgrep evolution
This would return the process id number only which you can then scan for more accurately with:
ps -ef | grep <PID>
# or, both in one go
ps -ef | grep $(pgrep evolution)
It may also be worth checking things like Calendar as well.
Not really sure how to check the calendar - I don't use it here and didn't touch it in Evolution. I use it on my phone for convenience, which isn't connected.
So, the pgrep command may return a list when there's more than one process found. In that case, the output doesn't work well with grep, so you need to search for each process individually. Use ps -ef | grep evolution or ps -ef | grep <PID> with one Process ID at the time to see processes are.
All right, I'll try what you're suggesting @zenzen , although I'm a bit unsure of what to do with the results.
I did try thinking laterally and tried using Bleachbit - and sure enough, Evolution IS still there and running BB didn't do the job of cleaning it or its cache, which is unusual. I've been using it for years and it's pretty powerful.