Do you use an agent's first name? Full name? Do you include a title e.g. Mr/Mrs/Ms? I usually go with the agent's full name: Dear Jane Doe... I read that using a title isn't necessary these days, so I don't include one. I'm not sure about just using their first name... Too informal?
This pertains finance recruitment, but most cover letters I receive are addressed "To whom it may concern". Though mind, candidates don't precisely know who will interview them.
I think you're fine with "Dear Jane Doe." This isn't something you can easily mess up so don't overthink it. It's the part that comes after that that matters. However, I once wrote "Dave" instead of "David," and that didn't seem to go over well. So, make sure you've got the name right. When submitting to some publishers I tend to leave off a name altogether and just start right in with my cover letter. This approach hasn't been a problem, but when contacting agents I would use their names.
Cheers Deadrats! I read that getting an agent's name wrong is a big turnoff. Some agents don't bother to read the rest of the submission. I always make sure to double check the spelling these days.
I think the turnoff part is true everywhere: you get a submission or an application for a job (or anything else) and on the first line there is already a mistake. You wonder "Is this person sloppy?" "Does this person not care?" "Will this person make the necessary effort to get things correct if needed? "Is this person just sending the same letter to everyone?" All questions imply a lack of interest or superficiality in the attitude of the applicant. I would feel turned off. To increase my willingness to double-check any submission or application, I focus on the idea that the reviewer is looking for reasons to dismiss any letter, because too many people apply for the same "position". All in all, I believe queries are short, thus precision is the standard (to be expected). This means you can only fall short from that. With that said, mistakes happen, and an agent might think one mistake is ok this time. The game of getting things correct is about getting as many chances as possible at having your novel read.