IPhone – How to transfer iMessages to the computer for archival

What happens in your proposed case is that if you delete messages from the iPhone, and then power on your Mac, the Mac will not receive those deleted messages.

EDIT: Well, folks, I stand corrected. I certainly believed the above to be the case, but my tests proved otherwise. I sent several messages from multiple devices to other devices that were powered down. Each message was deleted before the recipients were powered back on. Although there was a significant lag in reception (one took nearly ten minutes), all messages that were sent were received, even those that were deleted.

Several of the messages were out of sync, which doesn't surprise me given the flakiness of the iMessage system during its infancy. However, to the original question, the answer is that messages, deleted or otherwise, eventually find their destination, even to devices that were powered down when those messages were transmitted.

(Hat tip to tubedogg for the correction.)

If you know the iMessage account of your contact here is a bash script of mine to retrieve text + images.

#Parameter is a iMessage account (email or phone number i.e. +33616.... )
if [ $# -lt 1 ]; then
    echo "Enter a iMessage account (email of phone number i.e +33616.....) "
fi
login=$1

#Retrieve the text messages 

sqlite3 ~/Library/Messages/chat.db "
select is_from_me,text from message where handle_id=(
select handle_id from chat_handle_join where chat_id=(
select ROWID from chat where guid='iMessage;-;$1')
)" | sed 's/1\|/me: /g;s/0\|/budy: /g' > MessageBackup.txt


#Retrieve the attached stored in the local cache

sqlite3 ~/Library/Messages/chat.db "
select filename from attachment where rowid in (
select attachment_id from message_attachment_join where message_id in (
select rowid from message where cache_has_attachments=1 and handle_id=(
select handle_id from chat_handle_join where chat_id=(
select ROWID from chat where guid='iMessage;-;$1')
)))" | cut -c 2- | awk -v home=$HOME '{print home $0}' | tr '\n' '\0' | xargs -0 -t -I fname cp fname .