VSFTPD using username[AT]mydomain? Is this possible?

Greetings!

I have a program which tries to FTP to my CentOS server to download files and do various other tasks the first time it is launched.

I have been unable to properly configure VSFTPD to allow this program to connect. I’ve set up users and tried to connect through various FTP programs such as filezilla and WinSCP successfully.

After sniffing packets with wireshark, I’ve found that credentials are being sent to the server as follows:

Via FileZilla:
USER: username
PASS: password
Login successful

Via my software:
USER: [email protected]
PASS: password
Login incorrect

Is there any way I can set up my VSFTPD server to accept a username followed by @mydomain.com?

This is very urgent, any reply is very welcomed!

Thanks!