Send Mail to an Email List with REXX, SMTP and Sockets

Written by Dave Briccetti

This tip demonstrates sending email to a list of addresses using REXX, SMTP, and TCP Sockets.

If you are a REXX, SMTP, or Sockets expert and you see any errors or possible improvements to this tip, please share your knowledge with me.

When the OS/2 Bay Area User Group lost its automated email mailing list server in November, 1995, I was forced to find another way to notify our members about our meetings. I had the email addresses in an ASCII file, dumped from our member database.

First I wrote a simple REXX command to call sendmail for each address in the list: arg MailingList do while lines(MailingList) rec = linein(MailingList)'sendmail -Ce:\mptn\etc\sendmail.uml -af msg -f daveb@davebsoft.com "',|| rec || '"' end This method was very slow, as long as a minute or more for each address, because:
 * sendmail was doing a great deal of domain name service activity, which generated a lot of traffic over my 28.8K bps modem to the domain name server at my Internet service provider
 * sendmail actually connected with each recipient's mail system, and often there were delays in connecting

OS/2 email programs such as Post Road Mailer and PMMail very quickly send the mail to an intermediary which actually delivers the mail. To send the mail these OS/2 email programs use the Simple Mail Transfer Protocol (SMTP). To create a communication channel, these programs use TCP Sockets, probably from C or C++ language.

I decided to use the same approach, but since I had recently discovered the REXX Sockets interface, I thought I'd give it a go with REXX.

Here's the result of running the program with only a single user email address in the mailing list file, with commentary interspersed. The lines in the larger font are the SMTP commands we are sending. 220-blob.best.net Sendmail 8.6.12/8.6.5 ready at Thu, 16 Nov 1995 02:57:09 -0800220 ESMTP spoken here This is what the mail server says when we connect to it. The 220 code tells us that all is well and we can continue. EHLO This is the extended SMTP Hello command which starts the protocol and identifies us. 250-blob.best.net Hello daveb.vip.best.com [205.149.171.251], pleased to meet you250-SIZE250 HELP This response (code 250) tells us that the server supports extended SMTP, including the two extensions, SIZE and HELP. MAIL FROM:daveb@davebsoft.com SIZE=776 We begin a mail message, identifying the sender, and providing the size of the message. The SIZE parameter is an SMTP extension, and we are supporting it because the server supports it. 250 daveb@davebsoft.com... Sender ok Again the 250 tells us things are going well. RCPT TO:daveb@davebsoft.com We specify the recipient. 250 daveb@davebsoft.com... Recipient ok All still ok. DATA We indicate we're ready to send the body of the message. 354 Enter mail, end with "." on a line by itself The 354 tells us to send the data. 250 CAA19942 Message accepted for delivery It worked. QUIT We're done with the SMTP conversation. 221 blob.best.net closing connection And so is the server.

Rexx Script
The complete REXX program follows. You can also get it in zipped form. /* ============================================================================ Send Email Message to a Mailing List Via SMTP, Using the REXX Socket Interface Written by a novice REXX programmer Dave Briccetti, November 1995 daveb@davebsoft.com, http://www.davebsoft.com May be used for any purpose Thanks to REXX expert Charles Daney and internet expert David Singer for looking over the code ============================================================================ */

parse arg MailingList          /* The name of the file containing one email address per line */ MailingList = strip(MailingList)

call SetConstants

/* Load the REXX Socket interface */ call RxFuncAdd 'SockLoadFuncs', 'rxSock', 'SockLoadFuncs' call SockLoadFuncs

if EstablishProtocol = FALSE then exit

/* The protocol initiated, we'll now send the message to each recipient */

call SendMsgToEachRecipient

/* QUIT ends the protocol */ CmdReply = TransactSmtpCommand(socket, 'QUIT', 1)

/* Close the socket */ call SockSoClose socket

exit

/* ========================================================================= */ SetConstants: /* ========================================================================= */

MessageFile = 'msg'            /* The name of the file containing the message to send */ SendingHost = 'yourhost.com'   /* Host of the sender */ SendingUser = 'yourid'         /* User name of the sender */ MailServer = 'mailserver.com'  /* Mail server */

CRLF                   = '0d0a'x TRUE                    = 1 FALSE                  = 0

REPLYTYPE_OK           = '2'   /* SMTP reply code first byte */ REPLY_START_MAIL_INPUT = '354' /* SMTP reply code */

return

/* ========================================================================= */ EstablishProtocol: /* ========================================================================= */

socket = ConnectToMailServer(MailServer) if socket <.= 0 then do say 'Could not connect to mail server' return FALSE end

CmdReply = GetCmdReply(socket)

if left(CmdReply, 1) \= REPLYTYPE_OK then do say 'Could not establish protocol' return FALSE end

/* Send the extended hello, in case this SMTP server supports SMTP extensions */ CmdReply = TransactSmtpCommand(socket, 'EHLO', 1) if left(CmdReply, 1) = REPLYTYPE_OK then do /* That worked, so enable extended SMTP processing. If      the response to the EHLO indicates support for SIZE, enable our use of that feature */ SmtpExtensionsSupported = TRUE if pos('250 SIZE', CmdReply) >. 0 | pos('250-SIZE', CmdReply) >. 0 then SizeExtensionSupported = 1 end else do /* The server didn't recognize the EHLO so we'll go with the regular HELO */ SmtpExtensionsSupported = FALSE SizeExtensionSupported = FALSE CmdReply = TransactSmtpCommand(socket, 'HELO', 1) end

if left(CmdReply, 1) = REPLYTYPE_OK then return TRUE else return FALSE

/* ========================================================================= */ SendMsgBody: /* ========================================================================= */

/* DATA tells the server that the body of the message is coming. It  should reply with a code meaning "go ahead." */

CmdReply = TransactSmtpCommand(socket, 'DATA', 1) if substr(CmdReply, 1, 3) = REPLY_START_MAIL_INPUT then do /* Send the data, followed by a '.' on a line by itself to      indicate the end of the message */ CmdReply = TransactSmtpCommand(socket, MsgFileContents || CRLF || '.', 0) end

return

/* ========================================================================= */ SendMsgToEachRecipient: /* ========================================================================= */

MsgFileContents = charin(MessageFile, 1, chars(MessageFile)) call stream MessageFile, 'c', 'close' MsgFileContents = strip(MsgFileContents, 't', '1a'x) /* Strip EOF */ /* MAIL FROM identifies the sender. The SIZE= extension provides the size of the message, to allow the server to quickly refuse messages bigger than it wants. */ MailFromCmd = 'MAIL FROM:' || SendingUser || '@' || SendingHost

if SizeExtensionSupported then MailFromCmd = MailFromCmd 'SIZE=' || length(MsgFileContents) CmdReply = TransactSmtpCommand(socket, MailFromCmd, 1)

if left(CmdReply, 1) = REPLYTYPE_OK then do while lines(MailingList)

/* Read the recipient's email address from the mailing list file */ RecipientEmailAddress = linein(MailingList) if RecipientEmailAddress \= '' then /* RCPT identifies the intended recipient of the message */ CmdReply = TransactSmtpCommand(socket,,           "RCPT TO:" || RecipientEmailAddress, 1) end

call SendMsgBody

return

/* ========================================================================= */ ConnectToMailServer: procedure /* ========================================================================= */

parse arg MailServer socket = 0

/* Open a socket to the mail server. (The Sock* functions are  documented in the REXX Socket book in the Information folder   in the OS/2 System folder */

call SockInit if SockGetHostByName(MailServer, 'host.!') = 0 then say 'Could not get host by name' errno h_errno else do socket = SockSocket('AF_INET','SOCK_STREAM',0) address.!family = 'AF_INET' address.!port = 25         /* the standard SMTP port */ address.!addr = host.!addr if SockConnect(socket, 'address.!') = -1 then say 'Could not connect socket' errno h_errno end return socket

/* ========================================================================= */ GetCmdReply: procedure /* ========================================================================= */

parse arg socket

CRLF = '0d0a'x

/* Receive the response to the SMTP command into a variable. Use more than one socket read if necessary to collect the whole response. */ if SockRecv(socket, 'CmdReply', 200) <. 0 then do   say 'Error reading from socket' errno h_errno exit end

ReadCount = 1 MaxParts = 10

do while ReadCount <. MaxParts & right(CmdReply, 2) \= CRLF if SockRecv(socket, 'CmdReplyExtra', 200) <. 0 then do       say 'Error reading from socket' exit end CmdReply = CmdReply || CmdReplyExtra ReadCount = ReadCount + 1 end

say CmdReply return CmdReply

/* ========================================================================= */ TransactSmtpCommand: /* ========================================================================= */

parse arg socket, Cmd, SayCmd

/* Send a command to the SMTP server, echoing it to the display if requested */

if SayCmd then say Cmd rc = SockSend(socket, Cmd || CRLF) return GetCmdReply(socket)