Dear Miss Snark,
A week ago an agent mentioned to me his new associate recently informed him there were over five hundred e-queries that hadn't been read; some over six months old. He was innocently shocked by this and told her to go through them all and respond as soon as possible. One of them turned out to be fantastic, and he wound up selling the book for a nice figure.
The point here is that while so many of us are electronically oriented these days, there are still a lot of people (including some excellent agents) who aren't. Unless the agent's guidelines specifically state they don't respond to e-queries unless they are interested, would this be an example of why it's important for writers to re-query if they don't hear anything? Would three months be a decent time frame to re-query? Or is it all just a matter of wait and see?
I despise equeries.
If an agent doesn't say they prefer e-queries, I'd always go snail with an SASE.
On the other hand, there's no logical explanation for letting six months slide by on email. The only advantage of equeries is they are fast. Fast to answer with a form letter, and fast to send.
The same rules apply though: a month on queries. I know that sounds like forever with equeries but honestly, some people let them stack up and then read them in batches.
The thing is though---during that time you are busily querying OTHER agents. Preferably ones who answer their email.