Text messaging, like email, is an very useful communication
tool. As with email, messages can build up on our devices
without attention by the user. Apple has an option of
auto-deleting messages more than 30 days old. To the best of
my knowledge there is no way to sync deleted messages between
Blocking Unwanted Messages
If the message is from a legitimate sender, such as a
political party, dentist, or retailer, one can often reply
with STOP and the sender will honor the request.
Block, Filter, and Report Messages on iPhone
Preserving a Message
If you want to save a message forever, make a screenshot (or
PDF) of the message.
End-To-End Encryption (EE2E)
End-to-end encryption (E2EE) is a system of communication
where only the communicating users can read the messages. In
principle, it prevents potential eavesdroppers - including
telecom providers, Internet providers, and even the provider
of the communication service - from being able to access the
cryptographic keys needed to decrypt the conversation.
Signal - Secure Phone Calling & Text Messaging
Signal messages and calls are always end-to-end encrypted
and painstakingly engineered to keep your communication
safe. We can't read your messages or see your calls, and
no one else can either.
Apple iMessage And Facetime & Privacy
We designed iMessage and FaceTime to use end-to-end
encryption, so there's no way for Apple to decrypt the
content of your conversations when they are in transit
between devices. Attachments you send over iMessage (such
as photos or videos) are encrypted so that no one but the
sender and receiver(s) can access them.
As a point of comparison, neither Facebook Messenger nor
Facebook WhatsApp are considered to be private or secure.