Spoiler alert: a letter of intent is not the same as a cover letter. They're similar (being letters and all, and focused on yourself), but are actually used in different situations. Your cover letter is what you write when you're applying to a specific job you found through traditional channels (online job search, referral, recruiter). It details why you're a great fit for this particular job. A letter of intent is what you write when you're cold-calling (leaving a resume without being solicited for one), or applying for a job in a more general situation, like a job fair or submitting your resume to a general pool. The letter of intent is similar in that you're selling yourself, but tends to be less granular about a particular position. Letters of intent are often more networking-related, or aspirational, than position-oriented. Because you may have fewer specifics in hand about what you're applying for and who will be reading your application package, it's likely you won't have the most personalized opener. That's okay! Be general, but professional, formal, and polite.
A Letter of Intent is a written document that outlines a preliminary agreement between two parties regarding the terms of a potential purchase or other transaction. The two parties can settle on certain terms while agreeing to continue to negotiate the other terms and details of the transaction before actually signing a purchase agreement.