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Questions tagged [smtp]

SMTP is the Simple Mail Transfer Protocol, the most recent standard of which is defined in RFC 5321. It's the Internet standard for sending and receiving email.

Some characteristics of SMTP (Simple Mail Transfer Protocol):

  • The default port is TCP port 25 and new submissions (MSA) is port 587.
  • Although depreciated, some services still use port 465 (SMTPS) to support legacy applications.
  • It is used to transmit outbound mail, and mail servers (which listens on port 25) receives mail on port 25.
  • It should not be confused with POP3 / IMAP which is an actual store for the e-mail. SMTP messages are received by the receiving server and then an MTA moves it to the POP3 / IMAP mailbox where it is normally retrieved using a POP3 / IMAP client.

See Also:

RFC5321

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Reverse DNS - how to correctly configure for SMTP delivery

I started a new service and we need to send emails to our customers (new account confirms, etc). My server is known as prod01.bidrodeo.com and resolves to 97.107.134.38 . For reverse DNS, 97.107.134.38 resolves to prod01.bidrodeo.com . However,…
Krystian Cybulski
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Send an email with an attached file using telnet or netcat

I often use telnet or netcat to connect smtp servers to send an email as a test. Does anyone know how you would send an email using telnet or netcat but attach a file as well? There are probably better ways, but I still want to know :-) I would…
Kyle Brandt
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postfix sasl "cannot connect to saslauthd server: No such file or directory"

I try to setup postfix with smtp authentication. I want to use /etc/shadow as my realm Unfortunately I get a "generic error" when i try to authenticate # nc localhost 25 220 mail.foo ESMTP Postfix AUTH PLAIN…
user97262
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What's the point of repeating an email address in "The Envelope" and the "The Header"?

I learned that both the FROM address and the TO address is repeated in a hidden element called the "envelope", and then repeated again in the "body". Question Why isn't the envelope data copied into the "header"? Why does this duplication exist,…
TLDR
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Gratuitous CRLF in Subject: line - why is it there, and is it legal?

I'm running into a problem with a NAGIOS system sending emails to a popular email-to-SMS service. The email-to-SMS service takes emails with text in the Subject: line, and sends them on to the mobile number encoded in the To: field. So far so…
MadHatter
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What is the best method for sending email on behalf of my clients' domains?

I wanted to know the best way to make my mailserver send emails on behalf of my clients' domains, without being greylisted and also avoiding bounce problems. I've been reading some other questions here, here and here but none explores all the…
dgaspar
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When exim4 sends HELO/EHLO, how do I configure which host name it sends?

Mails from my system are being rejected when the receiving server does HELO checking. I believe my system is sending the wrong domain name. I'm running exim4. Googling for anything about exim4 and domains yields a nightmarish list of irrelevant…
user10066
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Security risk of POP before SMTP

I received an email from one of our servers this morning (CentOS, with WHM running LAMP) stating: The server has POP3 before SMTP enabled. For security reasons, cPanel highly recommends that you disable this functionality. I have done some…
GeoffAtkins
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Schedule/queue large e-mails in Exchange 2010, defer until latency drops

My challenge We have Exchange servers at various sites, but also aboard ships. The ships are connected to our network through satellite links when at sea, but switch to WiFi bridges when in port. Due the high latency (500+ ms) and not-uncommon…
abstrask
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Detect spammers on my server

I recently got one Undelivered Mail Returned to Sender while sending my newsletter to one of my 1500 customers. My website uses a double-opt-in procedure to make sure, the user explicitly want to receive my newsletter. The error message: smtp; 554…
koseduhemak
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What does dis=NONE mean in an email's Authentication-Results header?

The following is from an email I received recently: Authentication-Results: mx.google.com; spf=neutral; dkim=pass header.i=@yahoo.com; dmarc=pass (p=REJECT dis=NONE) header.from=yahoo.com I've been reading about SPF, DKIM, and…
Alex Henrie
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Has anyone ever used SMTP site links?

A simple real-life question, inspired by a comment here: Active Directory has supported inter-site replication using SMTP instead of direct RPC since its first introduction in Windows 2000. But did anyone ever actually use it? If yes, why was it…
Massimo
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NOQUEUE: reject: RCPT from on freebsd and postfix

I am building a server using this config -> http://www.purplehat.org/?page_id=4 and when trying to test basic email capabilities I get -> NOQUEUE: reject: RCPT from when try to send a test email. Below are my related configs How to I get…
mine
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In postfix, how to enforce tls + auth over 587 while leaving tls optional for 25

I would like to host mail services for some domains. I have succesfully setup postfix to consult sql for those virtual domains. What I would like to do is: For connections on 25: Deny relaying (only deliver to recipients of my virtual domains) …
Paralife
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How can I configure Postfix to ignore relayhost for some domains?

Is there a way in Postfix to ignore the relayhost? I have something like relayhost = [smtp.domain.net]:587 Now for a certain domain I don't want to send it out to that relay but want it to just send from that machine. How do I have to configure…
Mike
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