First thing is access the email account the forum uses and send a email directly to somewhere not from ubb.
If it is a hosted email account you probably have a web address to access it directly for use.
If you have another personal email account send it there.
See if you get a returned email or that it delivers.
If it gets returned it will have some errors that may be helpful.
There are also lots of blacklisting services to check.
Googly blacklist you can enter email or ip to see the results.
Just remember that Isp's don't use every blacklist service and there are numerous ones out there.
