Undeliverable emails from mailing list signups

[Luxlife]

Recently, we have received a number of System Administrator emails regarding mailing list signups that are not able to receive the email from generated by the signup process. Most of the notifications are from System Administrator and have the following content and structure:

Could not deliver message to the following recipient(s):

Failed Recipient: [email protected]
Reason: Remote host said: 450 4.2.1 The user you are trying to contact is receiving mail at a rate that
4.2.1 prevents additional messages from being delivered. Please resend your
4.2.1 message at a later time. If the user is able to receive mail at that
4.2.1 time, your message will be delivered. For more information, please
4.2.1 visit
4.2.1 https://support.google.com/mail/answer/6592 d19si23578488oei.80 - gsmtp


-- The header and top 20 lines of the message follows --

Received: from 3dcwsvm09.sl.local (UnknownHost [10.80.133.254]) by 3dcsmtpvm18.3dcartstores.com with SMTP;


Does any one else have this issue? We have had a number of these recently and wonder if it is related to the 7.2.2 update.

[Luxlife]

We are still receiving these errors, sometimes several times a day. There are others from the "postmaster" of the receiving mail service letting us know the delivery failed. Does anyone else have this issue? We have never had so many mailing list signup errors.

[Toobusy]

I get them alot as well and just assumed that people used an invalid email address to sign up. Although I have tried the occasional email address with my own email and had it go through, so I'm not sure what the answer would be that's causing the issue. I can't believe no one else has this happen?