Of course it will work. Please, note though, GMX does not accept any e-mails from the domains web.de, aol.com, hotmail.com, msn.com or yahoo.com if these e-mails were sent by another server. Therefore no e-mail from e.g. yahoo.com will be accepted if it was forwarded by Spamfence.net.

To receive e-mails from the domains named above despite them being forwarded by Spamfence GMX suggests to disable this “safety mechanism”. Please check with your GMX account under 'Options -> AntiSpam'. There, at the top, you will find a box. By activating this you accept to receive e-mails from e.g. AOL.com via a different server.