An important part of being a Managed Service Provider is getting alerts from customer software and devices. I’ve been streamlining this lately and like this approach. Besides allowing you to send alerts, it also allows you to receive emails on behalf of the customer, e.g. if you need to set up an account for them at vendor.
1. Create [email protected] or perhaps [email protected] account. Configure forwarding to one of my email accounts. Do not keep forwarded email in Gmail.
Note You will probably need to Gmail to allow less secure apps. You’ll get an email warning you to “review a blocked sign-in attempt” from a less secure app, but I’m not sure that email is sent on the first blocked attempt.
Update As of May 30, 2022, per this page, the “Less secure apps” setting is no longer available. You can, however, enable 2FA and then set up app passwords for use with devices that do not support modern authentication.
2. Set up Windows SMTP service on a server inside the customer domain. Allow unauthenticated relay from the LAN only. Deliver to smtp.gmail.com. Outbound security uses Basic authentication on the [email protected] account. This is the only place you have to specify the password at the customer site.
3. Set up all alerts/devices to use the customer’s server as the unauthenticated SMTP server on port 25. Send emails FROM [email protected] TO [email protected]. Interestingly, in this setup, Gmail does not even save Sent mail, which is fine by me.
Now if you want to change the recipient address, the only thing you have to change is the Gmail forwarding address.
More on the SMTP service setup is here, except the first step, enabling POP, is unnecessary: