Shoosmiths wanted to reduce its risk of not being able to provide e-mail evidence in court.
Andrew Downie, infrastructure and operations manager at Shoosmiths, said the firm needed to ensure it was able to store and retrieve all e-mails in a tamper-proof way that would be acceptable as evidence in court.
"Courts take a dim view of any organisation that is unable to provide proof of business correspondence," he said.
Mimecast provides Shoosmiths with a ten-year e-mail retention archive, a continuity service in the event of any Microsoft Exchange downtime, and security in the form of spam and virus filtering.
Downie said over a three-year period the SaaS model will save Shoosmiths 20% on the total cost of ownership of the archiving software alone.
"Further savings will come from reduced administration costs because the services are managed externally and from our not having to buy and administer additional storage as our needs grow," he said.
Downie said Shoosmiths had chosen Mimecast because it enabled the firm to continue to benefit from the SaaS model as well as meet all its e-mail management needs in a single package from a single supplier.
"SaaS is a good model for e-mail management because it enables us to separate it from the rest of our IT, but at the same time it was easy to implement and integrate with our existing e-mail system," he said.