Cupertino-based Symantec Corp. said Wednesday that it has signed a definitive agreement to acquire MessageLabs, which develops online messaging and web security services. Symantec said it will pay approximately $695M in cash for MessageLabs, which is based in the United Kingdom. Symantec said that MessageLabs had approximately $145M in revenues during fiscal year 2008. MessageLabs provides email filtering and related offerings via software-as-a-service; Symantec says it has more than 19,000 clients, ranging from small businesses to the Fortune 500. MessageLabs will become part of a new software-as-a-service product group for Symantec.