"Yahoo has been trying to divest itself of noncore businesses, so selling Zimbra certainly makes sense," said Lydia Leong, a Gartner analyst.

Still, Yahoo deserves credit for not wrecking Zimbra, customers said. "Yahoo did less damage to the Zimbra brand and product than I thought they would, so I am grateful for this," Day said.

During its two-plus years under Yahoo, Zimbra's sales grew significantly, and it stayed on a healthy schedule of upgrades.

"Yahoo's management of Zimbra was outstanding. Yahoo pretty much left Zimbra alone, didn't starve it of capital, force their culture down Zimbra's throats nor milked Zimbra for every ounce of profits they could have," Stone said.

Time will tell whether Zimbra thrives as part of VMware. In the meantime, Zimbra customers are hopeful.