FORTUNE — Email marketing and design firm Campaign Monitor yesterday announced that it has raised $250 million in equity funding from Insight Venture Partners, for an undisclosed ownership stake. This deal has been a very long time coming.

Insight first contacted Australia-based Campaign Monitor back in 2008, as the result of an internal program that cold-calls possible investment targets (similar to what private equity firms like Summit Partners and TA Associates have). At the time, Campaign Monitor was a four-year bootstrapped company that was turning a decent profit. It appreciated the interest, but saw no need to take outside capital.

The two groups talked occasionally over the next several years, but Campaign Monitor maintained its equity independence. It also continued to gain market share versus legacy rivals like Constant Contact CTCT , acquiring more than 100,000 paying customers in 170 countries.

By late last year, however, Campaign Monitor decided it needed to supercharge growth. Not only by opening new distribution channels, but also by building  a sales and marketing effort that had never really existed.

So it called Insight, which jumped on the opportunity.

“One thing that really makes Campaign Monitor stand out is their design work,” says Deven Parekh, an Insight partner who led the deal. “I’ll bet you get lots of Campaign Monitor emails without knowing they’re coming through campaign monitor, whereas when you get a Constant Contact email you know it’s a Constant Contact email.”

Parekh adds that while Insight committed the entire $250 million — which represents nearly 10% of the firm’s latest fund — it expects to syndicate out part of the round to other interested investors. He declined to say if the deal gives Insight a control position, but did acknowledge that the round values Campaign Monitor higher than the reported $270 million to $300 million that IBM ibm recently agreed to pay for rival email marketing company Silverpop.

Sign up for Dan Primack’s daily email newsletter on deals and deal-makers: