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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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Exclamation marks being inserted into Emails at approx 1000 character mark

Have a .NET program that uses the System.Net.Main namespace to send an email via SMTP. Its on a customers site so from there it will go via a (series of?) SMTP relay servers before it reaches its destination. At the moment I have no information…
Ryan
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554 - Sending MTA’s poor reputation

I am running an email server on 77.245.64.44 and have recently started to have problems with remote delivery of emails sent using this server. Only about 5% of recipients are rejecting the emails, but they all share the following common…
Phil Wilks
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How can I set up sendmail to forward all mail to an external MTA?

We have multiple applications that currently talk SMTP to an external MTA. The emails have arbitrary destination domains (they're emails to be sent to our users), but all from the same internal domain (support@company.com). I want to set up an…
unknown (google)
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fake "from" field in an email

How can I manipulate the "from" field in an email and make the "to" user see something different then the actual. Example: really from From: TStamper@yahoo.com but they see From: Tremayne "Top Dog" Stamper I've heard its from manipulating…
TStamper
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How does a Reverse DNS lookup work with regards to spam filters?

I have heard that most spam filters use a reverse DNS lookup on the originating IP address of the sending SMTP server (or something like that) as part of the verification process. I want to make sure my emails will pass this check. How exactly can…
codeflunky
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Under what circumstances (if any) should an MX record point to localhost?

I'm thinking that there's absolutely no reason or justification for this, but before I open my mouth and get some admin in deep kimchi, I thought I should ask. Is there any circumstance in which an MX record should point to a loopback address? To…
HopelessN00b
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Can't get SASL auxprop/sasldb working with postfix/Ubuntu 12.04

I have an Ubuntu 8.04LTS system running Postfix 2.5.1. On that system SMTP AUTH runs fine. The contents of /etc/postfix/sasl/smtpd.conf are: pwcheck_method: auxprop auxprop_plugin: sasldb mech_list: PLAIN The SASL-related properties…
QuantumMechanic
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Amazon SES vs EC2 Smtp server

We have an existing smtp environment setup in an EC2 instance which is used to send Transactional emails like password reset. Now we have a requirement to send System emails to a large user base in the range of > 1000 emails per day. First question…
Rishabh
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IIS6 Virtual SMTP server isn't coming back up automatically after a system restart

I've got a virtual server running Win2008 RC2. I've set up IIS6 with a virtual SMTP server on it to be the mail provider for the websites I'm hosting there. It all works great, but if for some reason the server reboots (auto updates are still…
Julian James
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Name one good reason for immediately failing on a SMTP 4xx code

I'm really curious about this. The question (highlighed in bold): Can someone name ONE GOOD REASON to have their email server permanently set up to auto-fail/immediate-fail on 4xx codes? Because frankly, it sounds like "their" setups are broken…
Avery Payne
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Any gotchas for using multiple SMTP servers for a single domain?

We want to run the majority of our mail (inbound and outbound) through a third-party service provider. We also want to keep an SMTP server running onsite that will be used with existing automated senders tied to internal projects. A colleague…
user31610
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SNI for a SMTP server

Let's say I have a dedicated server with some IP (IP1). I'm redirecting multiple domains (say example.com, example.net) to that IP via DNS. I've a single nginx server running here, and I've set up SNI correctly here and it works for HTTPS. I've also…
xryl669
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Fixing starttls verify=fail, verifymsg=unable to get local issuer certificate

Running Amazon Linux on EC2 instance with sendmail. I have an email account with Network Solutions, and use that account as a SMART_HOST relay in my sendmail configuration. It works well except for one little detail. In my maillog file I see…
sootsnoot
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Postfix NOQUEUE: reject: RCPT from unknown

I built a web based application but when it is trying to send an e-mail it fails. Postfix logs the following in it's mail.log: postfix/smtpd[22261]: warning: hostname srv.eastinc.nl does not resolve to address 192.168.3.101 …
Steve
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Logwatch is not respecting MailFrom

I've gone through today to setup Logwatch on my server and have installed this all successfully. I've followed this guide on Digital Ocean and set the MailFrom parameter to: MailFrom = mailer@mydomain.com I'm using ssmtp to send emails using my…
James
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