商务书信中恰当的招呼用语，也就是称呼语既要考虑到与收信人的熟悉程度也要考虑到信本身的正式与否。

Salutation should be considered on the basis of your familiarity with the reader as well as the formality of the situation. As a general rule, if the writer knows the reader well, he can salute the reader by the first name (Dear John). Salutation by the family name is, however, appropriate in most cases. 

When a department or the whole company rather than an individual is addressed, the following salutation fits well: 

Windsor Knitting Mill, Inc.
315 commercial Way
St. Louise Missouri 63108

Ladies and Gentlemen: or Dear Sir or Madam: 

Take particular care that the sexist words such as sirs, gentlemen and madam are outdated and very inappropriate in business today. Hence you´d better stay away from using the following salutations which might get you into trouble with some readers. 

Dear Sirs: Gentlemen: Dear Messrs. To Whom It May Concern: 

The correct punctuation for most business salutation is colon. Sometimes comma can also be used if you are on good terms with the reader. Be sure never to use semicolon.