For seamless saving and transferring of emails, IANA(The Internet Assigned Numbers Authority) has laid out some protocols for Electronic Mails.

Here is the detailed description of primary E-mail protocols which include IMAP, POP3 and SMTP.

It facilitates to receive emails from remote server to a local device.

The emails are downloaded and then removed from the server and transferred to a local device.

This reduces the space occupied by your account on the server.

It gives access to email on the web server from a local device.

This kind of protocol is useful if you have a business account.It allows the mails to be accessed by multiple clients.

IMAP works on Port 143 and Port 993 Port 143: It is a non-encrypted port.

It works on four ports: Port 25: This is a non-encrypted port that is set by default.

Port 2525: In case Port 25 is filtered, the SMTP will work on this port for non-encrypted messages.

Port 465: This port can be used for connecting to SMTP securely.

However, it is not recognized as a valid port by Internet Numbers Assigned Authority (IANA).

Click on the icon and from the available options, click on settings.

Some of the examples of Third Party Mail Client are Outlook, Thunderbird, MailList Controller and other accounts can also be connected in the same way.

Googles this extra layer of security is called Less Secure Apps.

Go to Connected apps and sites Enable Allow less secure app.

So, first, you will have to disable Two Step Verification for your account and then only you can enable Less Secure Apps option.

Unless it is not necessary, Do Not enable Less Secure Apps option.

Gmail Pop Account Settings For Mac Mail