IT shops should stick with service providers that have multiple Tier 4 data centers, and can promise replication between sites for redundancy, Forrester analysts Stephanie Balaouras and Christopher Voce write in a June titled "Protecting Email with the Cloud." 

"If you do an Internet search for 'online backup,' you will find dozens of providers," Forrester says. "But not all providers have 'telco-class' data centers, and some don't even bother to have alternative sites of their own."

Forrester says its clients typically say security is the biggest roadblock to adoption of software-as-a-service. "Beyond ensuring that your data will be encrypted in flight and at rest, you should also ask your service provider if it has a SAS 70 Type II as well as certifications for ISO standards … that spell out specific auditing requirements for hosting and security customer information," Forrester advises.

That being said, there are several advantages to using e-mail continuity and recovery services, particularly for companies that lack a second data center, the financial resources to make new up-front and ongoing investments, or the expertise to implement and manage a new disaster-recovery rollout.

E-mail recovery services are being offered by several types of companies, such as hosted mailbox providers; e-mail supporting service vendors such as Dell MessageOne, Global Relay and Symantec/Message Labs; disaster-recovery service vendors such as IBM and SunGard; and online backup vendors such as AmeriVault, i365 and Iron Mountain.