I've developed a sudden interest in whether an inability to DCC send files while being entirely able to receive them when everything at your end is configured correctly has much to do with the written policies of any ISP/School/business/etc. or is just unintentional/incompetent configuring at their end.
My guess is that an overwhelming majority of cases would be the latter, but it is only a guess, so can anyone quote references forbidding the use of passive mode to send files, either application specific, or regardless of the application?

It is mostly experienced by broadband users that run networks/routers where Network Address Translation is employed. If I receive a file it is fine, if I try to send it disconnects my IRC connection though the connection to the 'net itself remains fine.

There's a few ways around it but each one involves making the LAN more open to exploitation by hackers, something that I am not prepared to do just for the sake of sending files which can be emailed or uploaded to my website for distribution.

Distribution from a website is the best option because the user can get the download at a time of their choice and if you are intending to give the file to any people it is also cheaper. In the Australian experience there is no reputable long-standing companies providing unlimited bandwidth for brodband these days, even though there are a few small niche providers experimenting with re-introduction of the unlimited plans. Whereas I get 12GB of bandwidth from my website per annum for AU$275.00. There's no contest.

People are free to run mIRC's DCC server or open/forward ports for DCC, but as I said before, I believe that this leaves a LAN open to exploitation.

i wouldnt want to guess on stats of incompetant configuring vs intentional blocking of uploading or try to guess/assume which is the case in a general statement. There are however isps/businesses/schools that allow incoming dccs but object to sending them. In some cases i imagine its a security issue, in others a means of limiting bandwidth useage by those who want to run fservs. Wouldnt surprise me if there isnt an element of hrm, best not block downloading right now or we'll lose business, so lets block sending to cut down on bandwidth useage and see if that flies. If an entity wants to restrict the use of sending, seems to me that would include any and all means.