The ITL file is used for certificate-based trust between the phone and the Cisco UCM TFTP server. If the ITL file is invalid or missing, the phone cannot securely communicate with the TFTP server to download its configuration.
To resolve this, the administrator must manually delete the ITL file from the phone. This forces the phone to request a new ITL file from the TFTP server during its next boot.
Steps to Delete the ITL File:
1. On the phone, go to Settings > Security Configuration > Trust List.
2. Select ITL File and delete it.
3. Restart the phone to allow it to re-download the correct ITL file and configuration.

https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/expressway/admin_guide/X14-0-2/exwy_b_cisco-expressway-administrator-guide-x1402/exwy_m_introduction.html

When Mobile and Remote Access (MRA) is used with Cisco Jabber, remote users can access Cisco Unified Communications services without a VPN. This includes features like voice and video calling, instant messaging, presence, and visual voicemail.
Visual voicemail allows users to see a list of their voicemails, listen to them, and manage them directly from the Cisco Jabber client.
MRA works through Cisco Expressway-E and Expressway-C, ensuring secure remote connectivity while maintaining enterprise-level security and compliance.