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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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Postfix - Host or domain not found

I've just installed Postfix on my Ubuntu, on a local network. On this network, I have an Exchange Server (using domain mail.example.com). I had a problem sending an email to a local address: adress@example.com: relay=none, delay=0.01,…
Vincent LITUR
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What host name should the SSL certificate for an SMTP server contain?

I have a server foo.example.com at 192.0.2.1 It runs exim to receive e-mail for several of my domains. My domains each have an MX record pointing to mx.example.com, which resolves to 192.0.2.1 If I want to make exim offer TLS encryption for incoming…
David North
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Fixing My MTA's Poor Reputation

I have a web site that needs to send email to customers to deliver files that they have purchased. Reliable email delivery is vital to this business. Unfortunately, most of the emails sent by my server are not delivered due to my MTA's "poor…
Alex Reisner
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What are SMTP relays and smarthosts?

What exactly is an SMTP relay, and what exactly is an SMTP smarthost? Can someone give me a brief description of each, including how they relate to one another?
LanceBaynes
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Postfix Temporary lookup failure

I am trying to set up postfix, but I get a "Temporary lookup failure" error main.cf: inet_protocols = ipv4 inet_interfaces = all queue_directory = /var/spool/postfix command_directory = /usr/sbin daemon_directory = /usr/lib/postfix data_directory =…
dzervas
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Are two periods allowed in the local-part of an email address?

A third-party email gateway relay is refusing to process a message for an email address we're sending to. The address is in the format of firstname..lastname@recipientdomain.com (note the two periods). Is this allowed by RFC guidelines? RFC 2822…
Mike B
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Is an IPv6-only MTA possible yet?

Has anyone had tried to run an IPv6-only SMTP engine? Pretty much everybody with any sense has IPv6 configured for major front-end servers. I was curious if anyone had tried to run an IPv6-only MTA and received any connection errors. Is IPv6-only a…
joe
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Is it possible to send and receive an email from an IP address instead from a domain?

Usually an email has a domain name on the right side of the @, so you can identify an organization or a company. This domain is in fact nothing other than a "name" or an "alias" for an IP address, resolved by the name server. I think this could be…
user242212
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How to fix "unable to qualify my own domain name (myhost) -- using short name"?

and yes, I have 127.0.0.1 localhost myhost.mydomain.eu myhost.domain2.eu localhost.localdomain 127.0.1.1 myhost in hosts file. What is wrong? Sendmail started to put this error into log. May 9 19:08:54 myhost sm-mta[17103]: unable to qualify…
user107788
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Correct use of SMTP "Sender" header?

Our web application sends email messages to people when someone posts new content. Both sender and recipient have opted into receiving email messages from our application. When preparing such a message, we set the following SMTP headers: FROM:…
Eric Rath
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Google SMTP Error: 454 4.7.0 Too many login attempts, please try again later

I discovered that while it was possible to use Gmail/Google Apps as an SMTP server for scripted use, if too many emails were sent I started getting error messages: SMTP Error: 454 4.7.0 Too many login attempts, please try again later. Usually if I…
AlexMax
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How to Setup Ubuntu Mail Server with Google Apps?

I have a domain, let's call it foobar.com. All of the MX records for foobar.com point to Google's mail servers because I am using Google Apps for your domain to manage it. It's great because everyone gets all the advantages of GMail, but our e-mail…
Apreche
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What is preferable, "no-reply@" or "noreply@"?

Having a service that sends out notifications to users, I'm currently thinking about changing the sender email address from "info@" to something more meaningful. Since a reply never makes sense, I'm thinking about using one of those "no reply" email…
Uwe Keim
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Is it still "wrong" to require STARTTLS on incoming SMTP messages

According to the STARTTLS Spec Section 5: A publicly-referenced SMTP server MUST NOT require use of the STARTTLS extension in order to deliver mail locally. This rule prevents the STARTTLS extension from damaging the interoperability of the…
jackweirdy
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Easiest way to send a test email from a server, to test settings?

Using Windows (2008) is there an easy command line tool that I can use to send a test email from a server to test the SMTP, user authentication, ports, etc... without writing my own?
Jason
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