A real estate agent recently asked whether routing Follow Up Boss emails through Sendgrid was the right move. They were already using Sendgrid successfully with another system, but once they connected their domain to multiple platforms - FUB, Sierra Interactive, and a marketing provider - email issues started showing up. Deliverability became inconsistent, and fixing it took months of cleanup and expert help.

This is a common scenario once multiple systems start sharing the same domain and sending infrastructure.

When multiple platforms send email through the same Sendgrid account without separation, everything blends together. Engagement, complaints, bounces, and volume from one system directly impact the reputation of the others. If Sierra Interactive performs well but Follow Up Boss underperforms (or vice versa), Sendgrid and inbox providers don’t distinguish between them - they just see one sender reputation tied to the same IPs and domain.

That’s where things get tricky.

The right way to run this setup is to architect Sendgrid intentionally. That means using separate subuser accounts, assigning dedicated IPs, and routing each system through its own API key. This allows you to clearly see which platform is performing well and which isn’t. Once you have clean data, you can make informed decisions - either fixing the underperforming system or gradually merging traffic to let stronger engagement lift weaker senders.

My opinion is simple - routing everything through Sendgrid is the right approach, but only if it’s done correctly. Treating Sendgrid like a generic SMTP relay is how reputations get damaged and deliverability becomes unpredictable.

Email delivery today is not guaranteed. It’s earned. And the architecture behind it matters more than most people realize.