Have you tried enabling the scan confirmation report to obtain an error message, click here for those instructions.
If you are still having issues after trying these steps, I suggest that you call into our support department for assistance @ 1-800-821-2797.
I have an Altalink C8145 that I have setup SMTP using the same settings as a C8045. The test email function from web broswer passes but when I try to send an email from UI if fails. I have rebooted the copier. Powered off for 2 minutes and powered on. I have verified that the DNS/Domain name and TCP/IP settings are correct as well as the date/time. The hard drive was just replaced and the firmware is 113.010.001.06011. I tried cloning the C8045 email only settings into the C8145 but the clone fails.