I don't have that 3com product, but I know that as a general matter, many things don't work with Gmail due to the high-security requirement - SSL authentication is required in order to send through the smtp.gmail.com server. If there are no settings there for that, it probably won't ever work for you. First thing to try is to use your whole Gmail address for the username, but that is not the problem here, I fear.
One way I got around Gmail's SSL requirement recently for a scan-to-email copier that didn't have SSL was to set up mail service on an underutilized server which could do the SSL required for Gmail, and then I set it to relay mail only from the IP address of the copier in question.
You may find talk of an alternate Gmail SMTP server that does not require the SSL, but as far as I can tell, that is no longer valid, I could not get that to work.
Good luck.