in turkish, greeting are usually kept to the end of the letter rather than the opening.
still, greetings is selamlar or saygılar may be used which actually means "I/we offer you my/our respect"
ouch, this is a bad translation, it is something like respectfully but has a similar sounding as greetings (respects). hope this helps.

1) Selamlar(pl.), selam (sing., merhaba (origin: Ar.): a)Hi! b)Hi to everybody. c)Hi, there (in the beginning of a letter).
2) Selamlar: Respectfully yours (in the end of a letter)

In this case, I think it is used to mean "Hi There!, Hi everybody" in the
beginning of a letter, where "Merhaba" may be the best and commonly used in written Turkish.

If it's a bussiness letter, the beginnig should be formal and "saygılar" is the best word to give the same official meaning of the word "greetings". Hope it helps.

if you are at the end of a letter then you must use "saygilarimla". if you are at the beginnig of a letter you must say "saygilar". if it is a little informal then you can use "selam(lar)"

When 'Greetings' is used in the opening of a business letter, it means 'Merhaba' in Turkish.

When it is used in the end of a business letter, it means 'Saygılarımla' in Turkish

a Formal way of greeting for the introduction of a speech,visit ,letter,etc.(like Hello)