How to implement PHP webmail group.

How to implement PHP webmail group. You need to implement an Insite email function, but the group sending does not know how to do it. please help or who has examples for reference?

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Two methods
NO1. send a message to 'true' all users.
NO2. get the to-do task of the program when the user logs on.

Two methods
NO1. send a message to 'true' all users.
NO2. get the to-do task of the program when the user logs on.

The first method is not feasible. if there are too many people, the database will not be able to stand it. Can I elaborate on the second method?

The simplest way is to view the notification sent by the administrator in the everyone list.

Create a message table. After each user logs on to the message Table, find out whether or not he has provided it to himself. The flag is changed after reading.
Message publishing concurrency is not too large, and a large amount of data can be sharded by time, only concerned with recent
You can also use redis

If you are too lazy, create a new "notification" database. you can load it after logging on to the database.