Using the salutation “To Whom It May Concern” may be used in the most formal situations when the direct receiver is not known. The salutation “dear” is appropriate in formal business situations. If the recipient’s gender is not known, use the person’s first and last name in the salutation line.
When writing to colleagues you are familiar with, the salutation “hello” followed by the recipient’s first name suffices. Business e-mails sent to numerous recipients may be addressed as “Greetings All," “Hi All” or “Hello Team." For groups up to four people, it is appropriate to list all names in the salutation.