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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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Prepend X-header to all relayed messages in Postfix

I've got several production servers running a LAMP stack. They each have a local Postfix server catching any mail from the system and from PHP, and relaying it via a smarthost (the SendGrid SMTP service). I'd like to add a custom header to every…
Martijn Heemels
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SMTP host name vs. domain in "From:" address vis-a-vis Email Deliverability

I'm trying to implement (or make sure that I'm correctly following) email sending best practices to improve deliverability, but the role of the smtp server's host name vs the domain name of the From: email address seems to be unclear, even after…
Jared Duncan
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Sendmail : ignore local delivery

I've a Ubuntu webserver with Sendmail as my MTA Currently when i email outside my webserver's domain e.g. example.com to something like gmail or any other email outside the example.com domain it works perfectly. I don't want my sendmail daemon to…
Derek Organ
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Setting up two Exchange servers to receive mail on their old domains while sending and receiving using the same new domain

The scene: A merger of two companies. One running Exchange 2010, the other Exchange 2003, both having Active Directory Schemas at Server 2003, SP 2. Short term goal: Establish a trust between both domains to allow each company to access each other’s…
Nathan Hartley
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sendmail vs smtp server

I currently don't have a SMTP server setup. However, in my PHP code, I send all my SMTP request to sendmail. Are there any down fall to using this procedure? If yes, what are the advantages of sending all the STMP request to a 'centralize' SMTP…
ltang
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How to configure NGINX as proxy for local SMTP server?

I am doing some testing with the NodeJS smtp-server module. It exposes a listening SMTP server on any specified port. SMTP usually runs on port 25, but in order to run the Node app as a non-root user, I am prevented from binding to ports below…
Ryan Griggs
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How can I test a SMTP server?

I received SMTP server information and credentials and want to test if they work. How can I easily test a SMTP connection on Linux using the command line? I know I can do this via telnet / openssl but this seems very complicated. So how to check a…
Alex
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Send test mail using telnet via smtps (465) port

Based on this guide I am trying to send a test email using telnet from linux https://linuxconfig.org/send-an-email-using-telnet but the connection immediately disconnects: $ telnet smtp.gmail.com 465 Trying 108.177.126.108... Connected to…
u123
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Relay Postfix email through another server for bounces

I would like Postfix to try to deliver an email itself initially and, only if there is a bounce, then try to send through a relay. The scenario is that we moved an existing website, with users we need to email, to a new server with a new IP that…
Shovas
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Can I safely remove all mail services from CentOS?

I've inherited 3 legacy shared servers all running CentOS. We no longer offer any email subscriptions from our servers and have migrated everyone to cloud services. These servers host about 60 WordPress sites each. Across the 3 servers I have the…
David
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Send mail without MTA, GMail, etc

Why doesn't it seem to be possible to send mails from the command line without any kind of SMTP server? All solutions that I found either use sendmail, postfix, etc. (those are SMTP servers as far as I understand it) or send it over GMail or some…
Shadowigor
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iptables port forwarding to server with different port

I am trying to port forward from one server to another. I have tried numerous iptables commands but they don't work. Am I doing something wrong? Here is my setup: VPS1: 1.1.1.1 SMTP Port : 25 UFW: OFF iptables policy: Accept All Hostname:…
Wundark
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Testing an SMTP server with SSL?

I want to be sure a SSL/TLS connection is really being made to my SMTP Server on port 465. (The Server is running on Ubuntu 14.04) Using:- openssl s_client -connect example.co.uk:465 I get the responses shown below... Notice I get the…
jradxl
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How to choose a smarthost based on From: address in exim4 on Debian

I want to route emails with the From: .*@host1.com through smtp.server1.com and emails with the From: .*@host2.com through smtp.server2.com. For the moment, I have smarthost configured with dpkg-reconfigure exim4-config so that…
mikhailian
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Sendmail: "TLS verify=FAIL", "554 5.1.8 : Sender address rejected: MX record not found"

Have been struggling for a day already and can't find solution. When try to send mails to some hosts: Jan 5 10:31:37 vps**** sm-mta[2192]: STARTTLS=client, relay=mail-x.*****.co.uk., version=TLSv1/SSLv3, verify=FAIL, cipher=DHE-RSA-AES256-SHA,…
Amundio
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