How to deal with the design idea of the letter in a station

The design idea of the letter in the station
The design of the letter within the station, the requirements are similar to, for example:

A to the B station letter, will create a dialogue, click Open Dialogue, is a and B chat records

Difficulty :

1,a deleted one of the chats, but B's chat record is not changed

2,a Delete the conversation, but the conversation of B does not change

Find MySQL table design ideas, thank you!!!
------to solve the idea----------------------
UserID User ID
Conten Session Content
Del Delete flag: 1 Delete

------to solve the idea----------------------
Table structure.
ID, type, own_id, user_id, content, status, Addtime, lastmodify

Type:1 indicates that 2 of the issued
OWN_ID: represents your Own ID
USER_ID: Indicates the ID of each other
Content: Contents
Status:1 Display 0 Delete
Addtime: Release Time
Lastmodify: Last Modified time (if not available)


When id=1 people send messages to id=2. After sending, the table is recorded as follows

ID type own_id user_id content addtime lastmodify
1 1 1 2 content release time modified
2 2 2 1 content release time modified

The first record indicates that Id=1 sent a message to id=2
The second record indicates that id=2 received a message from id=1.
When id=1 delete information, the list of id=2 information will not be affected, and vice versa.

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