SMTP Error 471
SMTP Error 450 4.7.1
SMTP Error 451 4.7.1
451 4.7.1 Greylisting in action, please come back in 00:02:00 [minutes]
This error is usually followed by "Please try again later." It is connected with the sender's server. It is usually caused by an anti-spam policy or by a bad automatic update from antivirus software.
To fix the error, contact the SMTP service provider you use.
SMTP Error 451
Requested action aborted — Local error in processing
A remote antispam filter might reject your request. Also, your internet provider may be overloaded, or too many emails were sent through your SMTP relay. The next attempt may be successful if the error still occurs — contact your SMTP provider.
SMTP error 451 may
Usually, the recipient's spam-filter sends this error for policy reasons, labeling your email as spam.
You can eliminate this error by asking a recipient to whitelist you.
SMTP Error 551
551 Sender address is not valid for your login
551 This mail server requires authentication before sending mail from a locally hosted domain
Sometimes this error occurs intending to thwart spam, but it is not always accurate. To solve this problem, contact your internet service provider to ensure that you are a certified user. Also, this error may occur if the user is not local or if the email address is invalid.
SMTP error 554
If you receive this error, it means that the recipient's mail server considers your email to be spam or your IP to be blacklisted on one or more lists on the internet. To eliminate this error, ask the recipient to whitelist you or take steps for your IP address or ISP server to be removed from Realtime Blackhole List.
Last Updated: 21.01.2020