SMTP Status Codes and Error Messages from Error 421 to 422


SMTP status code 421 – <Server name> Service not available – the sending email program should try again later or The SMTP service /server you use has a limit on the number of
concurrent SMTP streams your server can use
(also called SMTP Error 4.2.1)
SMTP Error 421 : The Mail transfer service is
unavailable because of a transient event. SMTP reply
421 can be caused by many things but generally indicates
that the mail server which returns this status code is
currently unavailable but may be available later.
For example, the server administrator may have stopped
the mail service to troubleshoot a problem, or the mail
server is right in the middle of rebooting, or the mail server
is currently processing too many incoming messages or
incoming requests, etc…. Note : “Mail Server” in this
case can be any of the mail servers on the message’s
route – the sending server (your server), the ISP SMTP
server, or the recipient’s mail server.
Clearly, if you repeatedly receive an SMTP status 421 then
the problem is no longer of a transient nature and you
need to investigate or inform the relevant network
administrator, ISP tech support, or the recipient.
SMTP Response 421 can also be received as a result of
your message server sending an email where the total
number of TO, CC, and BCC users results in a
number of simultaneous SMTP connections that is in
excess of the number of connections your ISP or
SMTP service allows. A typical error message for this
situation would be : “421 Too many concurrent SMTP
connections from this IP address; please try again later”.
Typically, when this happens your server will have sent
some of the messages (note that for all servers, each
email sent by a user always gets broken down into
individual separate emails to each of the recipients in the
TO, CC, and BC fields), and will automatically retry a little
later to send the remaining messages.

SMTP status code 422 – The recipient’s mailbox is over its storage limit or The size of the message exceeds the recipient’s size limits for incoming emails
(also called SMTP Error 4.2.2)
SMTP Error 422 : Either the recipient’s mailbox is over its
storage limit or the message delivery directory (folder) on
the recipient’s mail server is currently over a size limit
imposed by the Network Administrator (e.g. possibly as a
result of the mail server having been down for some time,
having been repaired, and currently in the process of
collecting thousands of queued up messages).
However, SMTP response 422 can also be received if the
email being sent is larger than the incoming emails size
limit in operation at the recipient’s mail server (particularly
when that recipient’s mail server is Exchange Server)

Above are list of SMTP Errors Codes and Status Codes along with Error and Warning messages from Error 421 to 422 received while performing certain operation against mail server applications or related products.

What are SMTP Error Messages?
Simple Mail Transfer Protocol (SMTP) is an Internet standard for electronic mail (e-mail) transmission. SMTP protocol is used for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP.

In general, each SMTP error contains the following information:
• The SMTP Status Code or SMTP Error Codes or SMTP Reply Codes
• The message text. This text is usually returned with the Error code. Some messages employ word substitution, where the word substituted represents the system-replacement of a term more specific to the occurrence.
• An explanation of how the error may have occurred.

Hope this was helpful.

SQLServerF1 Team
Information about SMTP Error Codes or Status Codes and Error Messages on Windows, Linux Operating Systems.


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