For users who still have issue with Gmail, you should go to the security settings, and activate the "Less Secure App Access" 

Check your Incoming mail server and Outgoing mail server,

Suppose you are using gmail server, then the parameters for

Outgoing mail server should be,

• SMTP Server : smtp.gmail.com
• SMTP Port : 587
• Connection Security : TLS
• Username : youremailaddresss@gmail.com
• Password : yourpassword

Incoming mail server should be,

• Server Type : POP Server
• Server Name : pop.gmail.com
• SMTP Port : 995
• SSL/TLS : True
• Username : youremailaddresss@gmail.com
• Password : yourpassword

Hope it work for you.

Hi Amr,

The problem maybe from your e-mail account. Check if your e-mail service has external application support enabled. this can be done by loggin in to your e-mail id as soon as you try setting incoming server or fetch e-mail. There will be related notification with steps to resolve the issue.