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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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Why Outlook, Hotmail and Live return 250 Mail queued for delivery, but they never deliver it?

Ok, i've been seeing this the last week, tought it could be gone in a few days by itself, since i wasn't blacklisted and my DNS entries are all ok, but when i try to send e-mails to some user at Outlook, Live or Hotmail, i get this: 2015-02-11…
Jorge Ferrari
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How can I configure my postfix server so reject_sender_login_mismatch doesn't block aliases of the main account?

I've recently setup postfix, dovecot, amavis and a suite of other tools using iRedMail, and I'm having difficultly authenticating to my outgoing mail server. The issue is this: xyz@mydomain.com is an alias to abc@mydomain.com. I authenticate using…
FilmJ
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SMTP sent E-mail not copied to Sent Folder

I discovered that some (few) providers don't copy into the Sent folder those E-mails which are sent from mail clients through SMTP. They only copy them to the sent folder if you send them from their web interface, everything sent directly through…
user9948
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Cannot send email from EC2 instance on port 587

I have written a mail service for our flask application that uses Celery and RabbitMQ to send emails (using gmail). I have got the celery consumer and producer communicating okay but I cannot get to send send emails. I am getting a socket.error:…
Tahsin Mostafiz
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Postfix relay host connection fails: timed out while receiving initial server greeting

I have an Elastix server box that I want to send email notifications of voice mails from. I'd like to send them through our company email (hosted by shared web host provider Bluehost). I have followed instructions on how to use Postfix as a relay…
MrPhilTX
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SMTP Server 550 Access denied - Invalid HELO name

A bank we're working together is trying to send us an auto generated email to our company's email but it keeps bouncing off with the following SMPT error: Status: 5.5.0 Diagnostic-Code: smtp;550 Access denied - Invalid HELO name (See…
Ye Myat Aung
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Timeout error in all my apps for every call to smtp servers

On my VPS (a tophost.it "TopServer" with Ubuntu 12.04 LTS), since a few days ago all my apps are became unable to send emails. All I could learn from the logs is that every request goes timeout. I then tried to simply call from terminal telnet…
Darme
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ERROR: Message not sent. Server replied: 354

On webmail every user gets error "ERROR: Message not sent. Server replied: 354" while sending mails. But mails are sent properly and reaches properly. Can you tell me where is problem, and why it is occurred? UPDATE: I found in some resources that…
user48058
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Exchange Connector Won't Send to External Domains

I'm a developer trying to get my .Net application to send emails out through our Exchange server. I'm not an Exchange expert so I'll qualify that up front!! We've set up a receive Connector in Exchange that has the following properties: Network:…
sisdog
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How to start SMTP virtualhost [SMTP Virtual Server #1] through powershell or command prompt

Because of some error on my server, my SMTP service [SMTP Virtual Server #1] stops. I want to create job which will run periodically to check the SMTP server status, if it is stopped then the script will start it again. I have used Start-Service…
Optimus
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SMTP Reverse DNS Mismatch

My dedicated server ns382087.ovh.net resolves to 46.105.98.72 and hosts multiple domain with several dedicated IP addresses. Each new IP address is added to /etc/network/interfaces Among them, the dedicated server hosts my domain grand-manitou.com…
TheFoOL
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How the Postmaster@domain address works

I'm very new to Exchange (in fact, an apprentice and studying it at the moment) and am wondering how the Postmaster@domain.com address works. An example: A smarthost configured with one mailbox, Postmaster@serverfault.com, with an *@serverfault.com…
PnP
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What might cause a user to receive duplicate emails?

One of our customers is receiving duplicate emails from our application, even though as far as I can tell from the application and SMTP logs, we're only sending it out once. What are some of the ways that an email might be duplicated between sending…
Gavin
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Is there a way to completely disable outbound opportunistic TLS support in SendMail?

CentOS 5.x SendMail 8.14.4 An overzealous network security feature is causing TLS negotiations to fail when my Sendmail server tries to talk to external hosts. This is causing sendmail to constantly requeue some messages because it won't fail over…
Mike B
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Exim TLS and Secure SMTP

I'm in the process of converting an existing mail server to support encrypted SMTP for our clients, but I've run into this brick wall with very little useful log data to help me forward. Everything works fine when using regular unencrypted SMTP;…
Richard Keller
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