Receiver email address problem
Sometimes, we send message/mail to other account by typing receiver email address. But, the receiver didn’t get that email/message. The reason behind this issue may be varied like server may reject the messages or mails or may be email address problem. These type of issues called as Gmail Error 421 You should check receiver address carefully.
Don’t use space before or after the email address
Sender must ensure that they entered right email address. If you have used space before or after the email address, you should reenter the email address again without white space.
Don’t use dots at the end of the email address
You should not use dots symbols at the end of email address; otherwise Gmail server will reject the mail.
Before sending email, you should check receiver’s email address. It is correctly typed or not. Read word by word and confirm it again whether it is right or wrong.
IP address blocked
When any email address has send spam mails to other accounts, Google blocks that IP address. If the receiver address has been blocked by Google, it will not receive mails.
Help & Support
Users of Gmail account who are still facing mail rejecting problem, they can take support of Gmail Customer service for more help & if you want to get rid of Spam emails in Gmail then visit here for easy steps.