SMTP Servers

I'm having a lot of trouble using my ISP's SMTP server for sending emails to certain address in Asia and when traveling in some locations. In some cases it seems that my ISP's SMTP (netfirms) is being blocked as spam by some of my client's ISP so I can not send directly to them without the email being bounced back. However when I send to the same address from gmail then it goes through so I am pretty sure its my ISP's SMTP server that is the problem.

I know that there are other options out there. Any recommendations? I'm willing to pay for the best option if needed but of course free is better....