How to fix error ” 551 Sender address is not valid for your login “

Solution :

If you are getting the error “551 Sender address is not valid for your login” when you try to send emails from your email client then you need to check the login details entered by you in your email client.

Kindly follow the below procedure to reset the mail id password.

[1] Access your control panel at https://www.yourdomain.com:8443 [ Example :https://www.servername:8443 ]
[2] Click on subscriptions.
[3] Click on control panel of that subscriptions.
[4] Click on Mail.
[5] Click on the mail id for which you want to reset the password.
[6] Change the password [ Give the tough password,which consist of alphanumeric characters ].
[7] Click on ok.