I have no idea how emails work on the webservers. If I've sent emails using osCommerce for example, is there a way of seeing a queue or a log file or emails sent? Any advice appreciated.
It depends what type of server holds your account. If it's Ensim server, then your mail logs are in /var/log/maillog (and you can access it only with root permission) If you are on cPanel server then sent emails are logged in /var/log/exim_mainlog (also can be accessed only as root). If you are on different type of server, your mail log might be in some other location or with some other name... If you just have a hosting account on that server, and you do not have full root access to the server, then you might not be able to check mail logs. Ask your hosting company support? Good luck.
Just one other suggestion that might help you. Do you have WHM (WebHostManager? If you do you will be able to view the mail queue.
just want to add more information in FreeBSD server which is using cpanel the log for exim was located at /var/log/exim/