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RFC defined SMTP Status Error Codes
SMTP protocol specific response code design provides some useful (numeric) codes used for reporting mail (delivery status) system errors (Protocol method of sending and receiving data).
SMTP is a simple ASCII
protocol.
SMTP is a protocol governing
electronic mail transmission and reception (sending and receiving emails
between mail servers).
Notes: ASCII is a standard
developed by the;
American National Standards Institute
ANSI
to define how computers write & read characters
--used by most OS (but not by Windows NT)
Operational Sequent of
SMTP
Simple Mail Transfer Protocol
How two
MTAs
(Message Transfer Agent) communicate with each
other using a single TCP connection?
- Email is delivered by the source host
(sender) establishing a
TCP connection to port 25 of the (recipient)
destination host and wait...
- An
email daemon speaking SMTP simple ASCII
rfc 821
listening at port 25 on the (recipient) destination hose identify itself and
tell the (sender) whether it will accept mail....
-
*If not*
Server-time-out--the sending
mail server terminate the connection and try again later, after a predefined
undeliverable attempts--any
undeliverable message will be returned with an error report containing the
first part (message
headers) to the sender.
-
If the (recipient) mail server is willing
to accept the mail, the (sender) mail server sends the email address of the
recipient...
-
If it is a valid recipient email address, the
(recipient)
mail server gives a go-ahead signal...
-
Message is sent and acknowledged
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