HOW TO WRITE SALUTATION IN ENGLISH LETTER (SALAM PEMBUKA) dalam surat Bahasa Inggris

In salutation you can write Sir/Madam 

and sirs being plural is never used in letters. Even if you address your letter to more than a single person, you still wrote your salutation as Sir/Madam.

To

1. Alan

2.Desy

Sir/Madam,

In a formal letter the word dear is almost never used. The use of word dear represents your inexperience with writing  formal letters. 

In informal letters we do not use the word Sir itself. We usually write the name of the person to whom we're writing the letter as the informal letter is meant for the people we know closely. 

For example, Dear Nancy (Nancy can be a friend's name or a family members name or name of someone you know closely.)

As an informal letter is written to someone we do not know personally ( usually for official purposes) so the person or persons should be addressed informally at all points in the letter.

 You can use "To Whom It May Concern" in the circumstances described by boozer  when you are  writing a reference for someone which is to be held by the individual and shown by that individual to interested parties such as potential employers.

We use "Dear Sirs" when  writing to a company without specifying a job-title within that company.

I'm writing to 'Davotion Corporation' to say how much I like their sport shoes, for example.

We use "Dear Sir or Madam" when w are writing to the holder of a particular position within a company and we don't whether the person is male or female. 

We might use "Dear Sir or Madam" if I was writing to 'Head of Customer Services, Davotion Corporation' to say their sport shoes fell to bits after only one wearing, and I want a refund. 

  According to Wikipedia, the free encyclopedia

A salutation is a greeting used in a letter or other written or non-written communication. Salutations can be formal or informal. The most common form of salutation in an English letter is Dear followed by the recipient's given name or title. For each style of salutation there is an accompanying style of complimentary close, known as valediction. Examples of non-written salutations are bowing (common in Japan) or even addressing somebody by their name.

A salutation can be interpreted as a form of a signal in which the receiver of the salutation is being acknowledged, respected or thanked. Another simple but very common example of a salutation is a military salute. By saluting another rank, that person is signalling or showing his or her acknowledgment of the importance or significance of that person and his or her rank. Some greetings are considered vulgar, others "rude" and others "polite".