Follow the steps below.
1) Open the IMail Administration Console with administrative rights.
2) Navigate to the Anti-Virus tab. Seen below.
3) Change the 'Update URL' from http://upgrade.bitdefender.com to the new URL below.http://ipswitch-759594bd-57cf-4d10-811d-cf607fe24078.2d7dd.cdn.bitdefender.net
4) Once this is complete make sure to Apply the change then restart the SMTP & Queue Manager services.
5) Once you've made this change you can verify the software is using the new update URL by checking the avupdate.log located in the IMail directory.