POP3 stands for Post Office Protocol version 3. POP3 is a standard mail protocol used to receive emails from a remote server to a local email client.
POP3 allows you to download email messages on your local computer and read them even when you are offline by moving them to your email client.
That means, if you access your emails using SMTP on multiple email clients, then only one of them will have your emails at a time.
So, it is recommended to use IMAP instead of POP3 to access your emails from any number of clients without removing them from the receiving server.