I recently started using Geary to access email on my Librem 5.
I never like to have notifications for new emails. I like to check for mail manually.
There is a bug in Geary which means that disabling the setting to “Watch for new mail when closed” does not work. It will continue to run and check for new mail after closing and it will continue to issue notifications.
If you quit the application by pressing Ctrl+Q, then it will quit and stop checking for mail, but if you simply close the window then it will continue to run, check for mail and issue notifications about it.
A suggested workaround was to make a copy of /usr/share/applications/org.gnome.Geary.desktop into ~/.local/share/applications and then edit the copied file so that DBusActivatable=false.
I did this, which seems to have worked around the issue for now.