In order to understand MaxBulk Mailer "Connection logs" you need to read RFC 821 (Request for Comments 821). It is a technical memo about SMTP protocol implementation. (SMTP stands for SIMPLE MAIL TRANSFER PROTOCOL).
SMTP protocol is a text protocol where a SMTP client (MaxBulk Mailer) talks to a SMTP server. Basically this conversation looks like this (This example shows how the client connects, send the sender data, then the recipient data and finally the message itself):
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Server:
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220 SU-SCORE.ARPA Simple Mail Transfer Service Ready |
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Client:
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HELO MIT-MC.ARPA |
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Server:
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250 SU-SCORE.ARPA |
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Client:
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SEND FROM:<EAK@MIT-MC.ARPA> |
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Server:
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250 OK |
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Client:
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RCPT TO:<Admin.MRC@SU-SCORE.ARPA> |
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Server:
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450 User not active now |
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Client:
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DATA |
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Server:
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354 Start mail input; end with <CRLF>.<CRLF> |
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Client:
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Blah blah blah... |
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Client:
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...etc. etc. etc. |
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Client:
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. |
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Server:
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250 OK |
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Client:
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QUIT |
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Server:
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221 SU-SCORE.ARPA Service closing transmission channel |
MaxBulk sends commands like:
- HELO <domain>
RCPT TO: <forward-path>
DATA
SEND FROM: <reverse-path>
QUIT
The server always answer with a 3-digits code and a message. For example:
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211
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System status, or system help reply |
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220
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<domain> Service ready |
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221
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<domain> Service closing transmission channel |
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250
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Requested mail action okay, completed |
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251
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User not local; will forward to <forward-path> |
and if an error occurs, the server message always starts with a 4xx or 5xx code like:
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421
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<domain> Service not available, closing transmission channel |
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450
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Requested mail action not taken: mailbox unavailable |
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451
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Requested action aborted: local error in processing |
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452
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Requested action not taken: insufficient system storage |
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500
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Syntax error, command unrecognized |
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501
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Syntax error in parameters or arguments |
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502
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Command not implemented |
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503
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Bad sequence of commands |
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504
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Command parameter not implemented |
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550
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Requested action not taken: mailbox unavailable |
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551
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User not local; please try <forward-path> |
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552
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Requested mail action aborted: exceeded storage allocation |
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553
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Requested action not taken: mailbox name not allowed |
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554
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Transaction failed |
For more information take a look at the SMTP response code list.
