Messaging apps cover one-to-one chats, group conversations, voice and video calls and the sharing of files and media. Organisations use them for fast internal coordination, contact with customers or citizens and, in some sectors, crisis communication.
Beyond the message content, the sovereignty questions concern metadata and identity. Many services tie an account to a phone number, upload the address book to find contacts and keep records of who communicated with whom and when, even where the content itself is end-to-end encrypted. Backups are another weak point, since a cloud backup may not be protected with the same keys as the chat. Staff often bring the convenience of consumer apps such as WhatsApp into work, which creates shadow IT and makes retention and archiving duties hard to meet.
For a European option, check whether end-to-end encryption is documented and covers groups and calls, whether registration works without a phone number, which metadata is retained, whether clients and protocols are open and independently reviewed, and whether federation or self-hosting is possible. Decide in advance how work conversations are archived or deleted.