ResponseCode 421 when sending to specific domain
I'm trying to send from my zoho mail account to another email on a different domain, and I keep getting errors bouncing back.
The message is quoted below. I've obscured the email addresses for security reasons, and to show the sending and receiving accounts.
This message was created automatically by mail delivery system.
THIS IS A WARNING MESSAGE ONLY.
YOU DO NOT NEED TO RESEND YOUR MESSAGE.
The original message was received at Tue, 19 May 2015 09:12:44 -0700
from {sending}@lenballantine.com [{sending}@lenballantine.com]
----- The following addresses had fatal errors -----
[Status: Error, Address: <{receiving}@quietcitydesign.com>, ResponseCode 421, Unexpected failure, please try later]
Message will be retried for 4 more day(s)
----- Transcript of session follows -----
Received:from mail.zoho.com by mx.zohomail.com
with SMTP id 1432049170094770.6693581523623; Tue, 19 May 2015 08:26:10 -0700 (PDT)
Message-ID:<
14d6cc8367a.e7f96bd7101429.8662027633232616895@lenballantine.com>
Date:Tue, 19 May 2015 11:26:10 -0400
From:Len Marshall <{sending}@lenballantine.com>
User-Agent:Zoho Mail
To:"len" <{receiving}@quietcitydesign.com>
Subject:Fwd: Getting Started with Data Science
Content-Type:multipart/alternative;
boundary="----=_Part_138521_580788803.1432049170042"