You're asking if full-fidelity migration is realistic, but that's the wrong finish line. Even if you pull it off technically, you'll just be replicating a data model from a legacy, on-prem system into a cloud platform designed for modern workloads.
The real-world approach I've seen work is treating the historical archive as a read-only, searchable artifact, not as a first-class object. The "Archive & Link" pattern fails when the link is a static URL. It succeeds when you build a search facade that treats the new CRM and the old email store as two backend datasources, presenting a unified result set. Users won't know or care which system an email came from if the search works.
The killer isn't the migration script. It's the ongoing maintenance of that search layer after the new platform gets its next major update and the schema drifts. That's where your "pragmatic" approach becomes permanent, fragile infrastructure.
Everyone's rushing to solve the search problem, but they're skipping the real issue.
You're moving *to Salesforce*. Even if you magically import everything with perfect fidelity, you're now storing it in a system with notoriously rigid data storage and usage limits. That archive will bloat your data footprint, hammer your API calls, and cost you a fortune in extra storage SKUs. Salesforce's idea of "email objects" is not your old CRM's idea.
The "compromise" isn't a technical limitation of migration tools. It's a financial and operational one imposed by your new vendor's business model. You're not just migrating data, you're agreeing to their tax on your history.
—aB
You hit the nail on the head that it's not just "nice-to-have" data, it's critical. That context is everything for support.
On your first question about full-fidelity migration: it's technically doable with enough custom scripting, but I agree with the later comments that the bigger issue is what happens after. Even if you perfectly map every email and attachment into Salesforce's EmailMessage object, you'll run into volume limits and a performance hit that your users will feel daily.
The "Archive & Link" model is where most teams land. The trick, which others are getting at, is that the link can't just be a URL to a PDF dump. You need a way to search that archive from within Salesforce, maybe with a Lightning component that hits a separate search index. Otherwise, that history might as well be on a dusty shelf. It's an extra piece of infrastructure, but it keeps the new CRM running smoothly.
ship it
Oh wow, that's a great point about the headers. I hadn't even thought about the "In-Reply-To" metadata for future automation. So if we lose that, any rules we set up later to flag, say, "unanswered emails in a thread" would just break, right?