Folks, I received
I Means what it says, remove the SMTP-conf, in your YAML, go to /Settings/Device&Services, check the SMTP Integration there, make sure it's configured correct
Another time, try to use the Search function in here, im sure you would have found this.
Also it's a good practice / routine to Read the Release Note,before hitting Update
After verifying your SMTP integration settings, You could go to your Automations and run them manually( or "provoke" them somehow ) ( Beside the one which call 911 ) 
When older YAML only integrations get updated and moved to being configured in the graphical user interface they will also import your existing yaml into the new GUI integration for you. All you have to do iis check that this worked correctly by looking in Settings -> Devices & Services -> SMTP. If it did then delete your SMTP YAML and restart.
Everything should keep working.
Clear as mud to me as well ...
I checked configuration.yaml and didn't find an reference to smtp ... Digging into my config I found that I had my smtp configuration in a notify.yaml linked to configuration.yaml with an include command.
So the error message could have been clearer ....
I went to the new smtp integration in my devices and services, clicked on one of the entries to check the configuration and it crashed my home assistant .... not a good start
(update) .. .after another restart I could edit the smtp info ... no idea why it failed first time. I was left with three old entities related to the old smtp configuration .. they showed unknown .. no delete option available for the entity so I just had to disable them .. probably leaving more old junk in my config.
Almost all SMTP notifiers work fine for me. The only thing is that I can no longer view my groupings.
- platform: group
name: mailto_all
services:
- service: mailto_person1
- service: mailto_person2
You can to move those to a notify group Helper. Entity-based notifiers don't create services.
EDIT: send_message doesn't work as an action for legacy Notify Groups.
Neither of them works. Group via the helpers in the GUI. The code is still pre-migration. I’m not mixing the two.
I found the SMTP documentation page frustrating at best. I submitted feedback and provided edits to improve usability.
I discovered that the recipient name, once entered cannot be changed internally. By this I mean that I changed it, but the change had no effect. I restarted HA after changing it, still no effect. Please confirm.
Using gmail requires an APP password that is painful to set up. This is probably true of other services.
If one is going to remove the service, if it exists in configuration.yaml it must be removed from there, too.