Send Keap Email via another Email Gateway
We're all having email deliverability problems with Keap. A significant % of messages coming from infusionmail.com (even with correct SPF, DKIM and DMARC records) get rejected or go to the spam folder or Gmail's Promotions tab.
I've been relying on Zapier to send important emails via SMTP to clients. That's how I guarantee the message will land in the inbox. But it gets super complicated when I need to send it from the contact owner's address. I also lose all tracking and reporting functions.
Maybe PlusThis could create a tool that allows us to choose a different email gateway such as Mailgun (I already have it for the Contact Validator Tool), SendGrid, SMTP etc.
The list of 3rd party apps to improve Keap is already huge. Calendly, TurboDial, Twilio, Zapier, PlusThis, Mailgun, Memberium. I do not want to add WeDeliver.Email to this list. I'd rather upgrade our PlusThis account to use a tool similar to WeDeliver.

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Tim Withers commented
The only way we could do anything similar to this would be to integrate with another provider.
The downside is that we can't pull email templates from Keap, and then send them off via a third party service. We could send generic emails, non-templated, with merge fields supported (similar to how we do SMS). This is likely not what you are envisioning.
We highly recommend reaching out to Keap with these issues and asking them directly for the ability to use your own SMTP service instead.