Lewycasino,
SMTP is, of course, the tool of the spammers and phishers. So if the ISP providing your email has any common sense, they will lock down the service.
So, have you checked your SMTP authentication settings ? Or have you only checked the server name is correct ?
Have you checked with your ISP whether they accept roaming connections ? (some ISPs lock down to source IPs from their own network).