yes, "they" allow me too. the problem is when they mess it up and everything* you send is rejected because you no longer have reverse.
also my isp is very big and you can't really reach the right people to fix unusual stuff and they will try to bullshit their way out
i had to contact RIPE to get the problem fixed and it took more than a month. meanwhile i had to route the mail through another box that still had a reverse mapping
(the reverse zone had 3 nameservers and only one was fucked) 2 were operated by my isp and the third by RIPE
*) about 1/3 of the mails were blocked because 2 ns out of 3 were good
(Not picking on you, but on all the people who think they can do mail delivery and receiving as an amateur)
I think today, there are only two practical ways of handling mail. One is to use an outside mail provider (who is the MTA and hosts = stores the mail). Examples of that are Google's gmail, Apples mac.com and me.com, the big ISP (where I mean connectivity providers, like your cable TV or phone company), and a few specialized ones. If you are using a GUI only (that includes tablets/phones), get any of the many mail programs that can be configured to work with that mail provider. If you are using a shell-based machine or need outgoing mail from a Unix-style server, configure a bare-bones MTA that sends all mail to a smartest at your mail provider. The disadvantage of this is that not all mail providers are willing to serve custom domains, in particular not for free.
The other one is to use a very competent ISP who provides well managed services such as DNS, reverse DNS, and all the crazy stuff required to run mail servers (DKIM, SPF, DMARC and all that). If you try to do this at an incompetent ISP, then all hell will break loose. Historically I have recommended sonic.net, but they are trying to get out of the ISP business, and become only a bandwidth (fiber to the house) provider, so I don't know what their future outlook is.
Trying to run a mail server as an amateur, without a staff that is very knowledgeable and can monitor/manage things 24x7 is pretty silly.
People will complain that I am pushing users to give money to the big evil cloud companies. Let them complain. The reality is that mail has become very complex, due to the spam abuse of the internet, which for real users needs to be controlled, and that is hard and complex. Free mail service just makes no economic sense any longer. Remember, if something is free, then you are the product; in the case of free mail (and that includes the internet's TCP/IP infrastructure transporting port 25 for free), the end goal today is either to show you ads or spy on you to hack into your bank account. The days when the internet was a friendly group of a few computer science researchers helping each other is gone.