I had this same problem recently.  I am using QB Pro 2019.  My operating system is Windows 10 64-bit.  I am using gmail for emailing invoices.  After a couple of years of flawless operation, QB would just close when I tried to send an email.  If I tried to go into SendForms to change the settings, QB would just close.  

The fix for me had nothing to do with my logo on the templates or anything like that.  I simply changed the program to run in Windows 8 compatibility mode.  That did the trick!  Everything is back to normal.  Emails work fine again.

So, why did this happen?  Maybe a Windows update?  Or maybe something else?  I did recently run Avast Cleanup.  Whatever caused it, running in Windows 8 compatibility mode took care of it.

Right-click on the shortcut and select Properties.  Then select the Compatibility tab.  You can either just check the "Run this program in compatibility mode for" box and select Windows 8, or you can click the button to "Run compatibility troubleshooter".  I ran the troubleshooter and the end result was to set it to run in compatibility mode for Windows 8.

I hope this helps somebody.