I use my own SMTP server for receiving, but for sending I use the ISP's server (I think I have seem to have read somewhere that not only Google but some other s

I use my own SMTP server for receiving, but for sending I use the ISP's server (I think I have seem to have read somewhere that not only Google but some other services as well, will not accept mail from dynamic IP addresses). I have not had problems that I know of, so far. Please tell me of whatever mistake I may have made of such thing.