In the good old days (like 2010) agents allocated 20 to 30 seconds to quick read a query submitted via snail mail. Then, just like now, unsolicited query letters or manuscripts would end up in slush piles where they'd sit for months until someone (often an intern) opened them.
Today, thanks to the digital age, queries are submitted via email, opened, and scanned within hours, days, or weeks of submission. Agents spend 5 to 10 seconds deciding to read beyond the "subject line," or delete the query and move on to the next one.
The challenge~ Many, as in thousands, of would-be authors shot gun their queries by email (or through the "contact" pages on agent websites), resulting in a deluge of them into agent in-boxes.
BTW: The ease of electronically submitting queries (and manuscripts) is one reason why some agents continue to request paper queries. They believe amateurs won't take the time to write a query on paper, buy a stamp/envelope, and snail mail it.
Therefore, since most writers end up in the "digital slush pile," it makes perfect sense for you to learn how to write an e-query that will grab the agent's attention quickly. You may have as many as 12 to 17 lines to introduce your presentation on a computer screen. Or, it might be only a few lines if the agent is reading your presentation on a tablet or cell phone.
Understanding this situation should give you even more incentive to spend the time to learn how to write a sizzling query with: 1) an enticing "subject line" that invites the agent to keep on reading. 2) two or three first sentences (first paragraph) that motivate the agent to read your entire query.
Agent "contact" pages~ Many agents/agencies now offer (on their agency website) a contact page which you complete, then click to send to them through their website.
You'll be asked to provide your name and email address, followed by a "topic" or "subject" line. What you write in that line is vital. It will either motivate the agent to read your query, or pass.
Then, when you tab down to the larger box, jump right into your query. Do not add the agent's name, or any type of a greeting.
Stick to your goal of "keep 'um reading." If you've written your query correctly, the agent will happily read every work in order to learn more about the project you offer.
At the end of your third paragraph (all about you), thank the agent for their time and consideration. That's it. Period. End of query.