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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

3133 questions
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mail loops back to myself | postfix

Hi I have an issue with bounced mail it does not happen all the time but at the same time is very frequent. Most of the time if I send an email to an address that does not exist then i get a bounce back into failues@domain however there seem to be…
Alistair Prestidge
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Roundcube & Postfix SMTP: SSL routines:SSL3_READ_BYTES:tlsv1 alert unknown ca:s3_pkt.c

I have a Postfix / Dovecot / Roundcube setup that I use personally, as well as provide to other users. I am attempting to transfer this entire setup to a new box, but having some issues. Mail receiving is working fine, (only tested internally,…
1n5aN1aC
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How can you test a backup / secondary MX server?

I'm wanting to set up a secondary MX server using Postfix but I am wondering what is the best way to test this prior to putting into production (by adding its MX entry)? One possible way is to test it with an entirely different domain name, ie buy a…
thomasrutter
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Should I listen for SMTP on both 25 and 587?

I was setting up haraka as our mailing server, and for outbound email, it suggests moving to port 587 for SMTPS auth support. However, I'm unsure if I should be running 2 instances of haraka on both ports, just listen on one (587), or listen on…
Nemo
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monit send email does not work

I am trying to use monit, and set up email server using gmail. The configuration file is like this: set mailserver smtp.gmail.com port 587 username "someuser@gmail.com" password "password" using tlsv1 with timeout 30 seconds And I set an alert to…
Jiechao Li
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Why is Postfix trying to connect to other machines SMTP port 25?

I get these errors: Jul 5 11:09:25 relay postfix/smtp[3084]: connect to ab.xyz.com[10.41.0.101]:25: Connection refused Jul 5 11:09:25 relay postfix/smtp[3087]: connect to ab.xyz.com[10.41.0.247]:25: Connection refused Jul 5 11:09:25 relay…
TryTryAgain
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How to configure php.ini with remote SMTP?

How do I configure PHP to send mail using mail() via a remote SMTP server? I've tried to do this using php.ini but it seems that you can only do that under Windows32 and I want to do this on my Unix server. Also I've tried to change the…
Brayn
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In the mail header, what does the "received from" ip refer to?

I noticed that some mail header contact a field called received : from and it contains an ip address. Does this address refer to the sender machine even if he is using a web interface or to the server ?
sohaibafifi
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What takes precedence: an SPF record with "-all" in the primary TXT record, or one in the "include" section?

Suppose I have a domain (company.com) with an SPF that looks like this: v=spf1 ip4:70.70.70.70 include:host.marketing.com -all and "host.marketing.com" looks like this v=spf1 ip4:8.8.8.8 ~all What takes precedence for company.com, the "~" or the…
makerofthings7
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smtp remote host responds "550 Sender verify failed"

A server I'm taking care of uses qmail for MTA. I can send and receive to almost every domain except one or two that give the following error, or something very similar: 550-Verification failed for 550-No Such User Here 550…
jfoucher
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Temporary failure in name resolution : Host name lookup failure

I've got a script in PHP that's been running fine for months. It recently stopped working. This script connects to gmail to send out an email to my customers. Recently, I started getting this error when I run the script: The SMTP connection failed…
GeoffreyF67
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Outgoing only SMTP server

I want to setup an outgoing only SMTP server on Debian, so my Web-applications will be able to send e-mails via it. I don't want to use another hosts because of security and customizability of my own setup. I wish to install Postfix and configure it…
Daniel O'Hara
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Trying to setup mail server, can't get ports (25, 587) to work

I've searched everywhere and I'm really struggling with this one. I think I've tried just about everything. Background info VPS with CentOS 6.7 Postfix 2.6.6 dovecot, amavis, mysql, fail2ban I've verified with my VPS provider that they do not block…
reachergilt
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Why does DMARC operate on the From-address, and not the envelope sender (Return-Path)?

Several emails sent from my webserver to a Gmail address, where the From: address is websitevisitor@gmail.com, have been marked as spam by Gmail. The From: field is populated from form data, and corresponds to the visitor's actual email address,…
EelkeSpaak
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MX priority server behaviour

This is a question about MX procotol priority. If I have two server as MX with different priority: MX 10 serverA MX 20 serverB Is this guarantee by the protocol that the MX 10 is the prefered? Can the submitter choose the secondary for any other…
Tobia
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