Which version of mail server are you using - In the past I noticed that if using Exchange 2003 SP1 (or later SP) that Authnenticated SMTP did not work - before SP1 the same Exchange server did work. Then I found that you could not use telnet to send an authenticated SMTP request either - so it appeared that MS chanegd something relating to Basic Authentication with the update.

The way I worked around it was to configure SMTP on the Exchnage server to allow anonymous SMTP access but then lock down the range of IP addresses that could access the SMTP server to the few internal servers I had that needed to send e-mails.

I use small business server 2008 with exchange 2007. Backup sent email until I had to change the user. Since then it doesn't send email anymore...

Was the earlier account same as Backup Exec service account? I would ensure that Backup Exec service account has permissions on SMTP.

Thanks

 You could try an SMTP telnet test from Media Server to Mail Server as per following article
NOTE: You will ned to Base4 encode your SMTP username and password to test this - the article suggests using perl, but google will probably locate loads of ways to do that

http://technet.microsoft.com/en-us/library/aa995718(EXCHG.65).aspx

Also note the telnet built into windows does not seem to like backspacing to correct typing mistakes - so make a mistake and you often have to start again

If the telnet test fails then the issue may not be with Backup Exec

I'd say you need to talk to an expert on your mail server and either make sure basic authentication is configured correctly so that the telnet test works and then try Backup Exec - or configure it for anonymous access (but make sure it is NOT an open relay on the internet)

WARNING: If you go open relay on the internet you could get blacklisted which would affect your company's ability to send and receive e-mails.