Watch this video to setup as many SMTP email servers as you want. And, then add as many Email Notification Nodes into your decision tree as you want.

When Using Google or G-Suite…
You can use emails associated with domains used with GSuite – you can’t use GSuite as your SMTP.
Click here > How to use emails associated with GSuite

31st AUGUST 2020: DUE TO CONTRADICTORY REQUIREMENTS BY GOOGLE AND UNREASONABLE INCREASED APP VERIFICATION REQUIREMENTS BY GOOGLE, GMAIL or GSUITE WILL NOT BE SUPPORTED AS AN SMTP.
Yes, you can send email from a domain you are using with Gsuite?
Absolutely, you can. You can use any existing or new email address on any domain you own domain including the one you’re using with Gsuite. You can also create a new email address specifically for use in a LeadsHook Email Notifications node.
You can not use your existing Gmail or Gsuite accounts because of onerous security requirements imposed by Google by requiring apps like LeadsHook to pay $8000 to $75000 for verification…
“Depending on the size and complexity of your app, the cost for the third-party assessment might vary from $8,000 to $75,000”
We have going back and forth for months to get LeadsHook verified. We have decided to not support email notifications through Gmail or Gsuite because its not needed and there are plenty of other much easier and cheaper solutions.
SendGrid
https://sendgrid.com/docs/for-developers/sending-email/integrating-with-the-smtp-api/
How to Create a Subject Line with Custom Fields
If the leads you send has the same subject line, then some email clients will lump all of your emails in ONE thread.
You can use this which contains custom fields so the lead id will contain a new number for each lead.
[{_c_dt}] New Lead ({lead_id})
{_c_dt}: Decision Tree Title
{lead_id}: Lead ID
Deleting SMTP settings
Take note, that you will need to disable the node that is currently using the SMTP setting before you can delete the SMTP itself.
You can do this by deleting the node or simply removing the SMTP settings from the node that is using it and republish the Decision Tree again.

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I’ve gone through all the steps for G Suite here:
https://support.google.com/a/answer/2956491
but I still can’t get STMP to work with G Suite.
I just used my gmail.com address and it works as described. But really would be great to be able to do this with a work email.
Hi Dan,
You can use any SMTP including your work one.
Please send an email to support and we’ll help you through the process.
You need to turn on 2 factor authentication and then generate the app password and normally that’s all there is to it.
Nik