Is it appropriate to start business letters with "Hello!"?

[Alyona]

What greetings can be used if the sender doesn't know time of day and the recipient's name?

 

[pink_is_metal]

No not really.
It's more friendly, you want to sound bold and determined rather than saying "hello"

 

[supermarum]

Kind of depends on the relationship with th business parts, doesn't it..?