Not that I can see. Both lets you setup multiple domains and aliases. Since Fastmail's datacenters appear to be in the US (New York region and Seattle), they'

Not that I can see. Both lets you setup multiple domains and aliases. Since Fastmail's datacenters appear to be in the US (New York region and Seattle), they'll end up falling under the same laws as Microsoft. Theoretically you might save a bit with Fastmail - it seems like you can have 1 standard account that is $5/month and owns the domain and then other basic accounts at $3/month that have an alias for the domain, but I don't know how that works in practice. For a large family the savings could add up.