Depending the ISP you use, port 25 might not even be available to you and if the port is available, there might be limitations in the amount of mails you are allowed to send per minute.
Besides that, there are external organizations that can (and will!) put your domain on a block-list, allowing no mail of any kind to pass (depending on the location of your mail server, different organizations take care of this).
You get a warning message with an URL that you can use to lift this ban, but if the same happens in the grace period...
This happened twice to me (yes I have my own domain with a dedicated Linux mail server, completely under my control), because of a virus that was sending messages all over the place.
So if you have the time to do the research, get a dedicated Linux mail-server. Very capable and free. If you don't want all the headaches that come with previous solution, see what kind of mail services you can get from your current ISP and let them do the work regarding maintenance, up-time etc.