Need Expert Linux Sys Admin to Scan my server for vulnerabilities and track possible sending of Spam MAIL, and check my mail server

Hello, There is one specific domain I host on my dedicated linux server. I keep getting emails to my personal GMAIL account from cpanelusername(at)[login to view URL] (this is just an example, and not a real e-mail) So.. since that is the default mail account for my cpanel account.. I changed that cpanel password.. and I am still getting spam messages to my inbox from that email. I clicked details.. and it said: mailed-by [login to view URL] signed-by [login to view URL] Does this mean it's DEFINITELY being sent by my server? (it shows my real domain URL) I have gotten no spam complaints.. and this has been going on for a week or 2.. not sure if it's spamming any other email.. or how my gmail account got on the list All the emails contain ads for viagra, and mostly this image: [login to view URL] [login to view URL] I need someone to check my server for any security flaws or vulnerabilities. I also want a search done to find any mail sending scripts, and if we cannot find it to setup some more detailed logging system to track down where it's coming from next time the mail is sent. This may be a very quick job for you, I don't think the box has any other security issues, it's very secure, but this script may have been uploaded with a client FTP or something.. The box is hardened and secure for the most part. Also, my server has always had problems sending mail to Yahoo and some other providers, please let me know if you know exactly how to fix this issue.. I don't think my IP is on a blacklist (or at least it wasn't 1 month ago when I last checked), butt if you have a solution please let me know. Thanks!