I'm going to disagree here. It's likely standard advice from agents not to query again with the same project, not to do it again unless there are changes to the manuscript, or not to do it again for a year.
Frankly, most agents do not remember and do not keep records. If your first attempt was just god-awful, it's likely they hit delete within a few sentences.
I wouldn't recommend re-querying more than once - so make sure your next attempt is GOOD - but I'd give it maybe 3 to 6 months. For best results, use a different email address, but it's not necessary. Here's what will happen:
- You will get a couple of slightly pissed-off emails from agents (or more likely agent's assistants) who don't delete all their emails. No, they are not going to share your name with all the other agents and black-list you or something.
- If your query is any good, you will get a second look from everyone else.
- If it's really good, you'll get a bunch of requests for more.
How do I know this? Because this is what I did. I currently have a very good agent whom I re-queried with the same email address after 6 months. I went from terrible query to very good query. He never even mentioned it.
Of course, this is all contingent upon your query being top notch and your sample being very good. So take some time and make sure both are up to snuff.