After the greeting is to introduce yourself and explain the reason why the sender writes to a stranger - to the recipient. Perhaps the most important rule - to save someone else's time. The phrase should be formulated succinctly, clearly, concisely. With punctuation, emoticons and slang do not overdo it. If literacy is lame, you should write simple sentences, without the engine verbal participle phrases after the first comma. Greeting better to choose a neutral, "Hello", "Hello".
The next paragraph is the main part of the letter, where the author explains his interest in greater detail, asks questions, thoroughly explains the issue. If it's a business letter, it would be appropriate to refer to two or three mutual friends or people who respected so that the recipient can verify the above information. If it is purely personal and delicate letter (for example, the addressee - a potential relative, classmate, or the person whose assistance is necessary), you should speak to the emotions of the interlocutor. For example: "I understand that You may be surprised to receive this letter" or "I hope you're not upset, but the situation..."
Third paragraph - the expression of gratitude and a common phrase in the spirit: "Thank you for paying attention and read this letter to the end" and "I hope for fruitful cooperation". Polite "tail": "sincerely" or "good" is valid, but would be better if it was a personal signature, not a template, scored in the mail program. Business man leaves his signature your contacts: the website of the company, the phones reception. Private correspondence means a link on a phone or a blog of any personal resource that will help to orentiruetsya in the subject line.
Correspondence with a stranger implies politeness, kindness and hope for a continued dialogue. The possible PostScript: "If You have any questions, happy to answer them."