Mail sending using web form , FROM my Domain Email account

Question

Dear all, I am using my own domain email account like [email protected] to send email from the asp.net web application , sometimes it send an email and some times it did not send an email randomly , i debug the code and it says cannot connect to the server IP{some IP:Port} so i contact the service provider and they said that the firewall on the server is blocking the IP due to shared hosting , so they suggest me to tell them all the IP address from where the request come to send an email , but the nature of my application is like that i do not know all the client earlier so that i can share the IP with hosting provider to white list them secondly they may have dynamic IP so i cannot share the IP, What would be the work around , I am using the NEXUS solution provider.