Some agents say if they don't see a reply-paid envelope right away they reject the query immediately. This is a big problem when querying American agents since many won't deal with IRCs and insist on US stamps. I spent hours trying to buy US stamps online only to discover the US Postal Service is 'not at this time accepting overseas orders'.
As for IRCs, Australia Post is not issuing any more. There's some new system planned, I'm told, but no-one seems to know what it is.
In my queries I mention these facts and ask if they'd mind replying by email. Of course, if they don't get that far into the query they might reject it first.
I'll start by clarifying that 'IRCs' mean 'International Response Coupons' for those who - like me - didn't immediately twig. And now I'm going to state that I wasn't asked a question, so I'm not really sure what I'm meant to say. I'll take a guess at a question, though:
'So what do I do when I can't send an IRC or American stamps?'
Well, you've already stated your problem in your query letter and asked the agents to respond by email. Whether they do or not is something you obviously can't control, so you're probably just going to have to risk it. There are also agencies who take electronic queries so you would have no problems there.
I anticipate that the day will come - soon - when agencies around the world will have to move beyond snail mail queries and embrace the digital age, ready or not. I personally find it a waste of time to send things back by post, SSAE or not. I'd love it if everyone queried electronically. It's much easier to organise queries when I can file them in folders in my email programme, and it's more environmentally friendly.
As for you, querying author, it's your decision as to whether or not you send queries to the luddites, and you'll just have to accept the consequences. The US and Australian postal services have obviously realised there's no money to be made in IRCs or foreign purchase of stamps because - guess what? - people use email.