I got the new solution for smtp.gmail.com now.
1. 2 Step Verification (2SV)
2. App Password
2.1 Generate password with
Select app: "Mail", Select device: "Windows Computer"
2.2 Get 16 digits password.
2.3 Use this password instead of gmail's password.
done.
Detlef wrote:Thank you, Dutch.
Unfortunately my client wants to stay at gmail.com to send invoices to her customers.
I' ll try to convince her to change to a service like mailjet.com as you did.
Have a nice weekend.
Regards,
Detlef