Server Fault Stack Exchange
Server Fault Stack Exchange

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

3170 questions
21
votes
2 answers

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
  • 493
9
votes
3 answers

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
  • 428
7
votes
2 answers

If a lower priority mail server only serves code 450, will sending servers on retry use a higher priority server?

I had a backup mail server eat a bunch of messages and I want to just configure a simple server to send 450 for all messages. However, I'm not sure this is a good idea because if the sending servers on retry do not attempt to send to the higher…
Paul
  • 3,137
6
votes
4 answers

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
  • 171
5
votes
4 answers

A flexible SMTP server that's open source or free

We currently have our own in-house email marketing software for our newsletters, and were using SQL server's SMTP agent to send emails through our local SMTP server (IIS) and then onto our ISP's SMTP Relay. The SQL Server was involved because the…
Khuram Malik
  • 183
  • 1
  • 5
4
votes
2 answers

How do I track whether a email was successful among thousands (IIS 6, .NET 3.5)

I want to be able to tell if an email sent to a user is successful or not. I've tried looking at the SMTP logs and there appears to be no way to link server requests with server responses. So if I get an error 550 and the attempted address is not…
Micah B.
  • 143
4
votes
1 answer

Is there a way for an SMTP server to respond that a user has moved to a new address?

Is there a way for an SMTP server to tell an MTA that a user has moved to a new address? There are many SMTP return codes, including for common situations like Mailboxes being full, the address not existing, the message being rejected etc. Is there…
mikemaccana
  • 3,470
3
votes
1 answer

SMTP error goes directly to Badmail directory after Queue

This is the error I got in the .BDR Unable to deliver this message because the follow error was encountered: "This message is a delivery status notification that cannot be delivered.". The specific error code was 0xC00402C7. The message sender…
Sergio López
  • 131
3
votes
2 answers

E-Mail blocked because of IPs in Trace-Fields ("Received")

we have an SMTP problem. Our setup is a internal Exchange server and an external mail gateway (exim) with a DNS entry and MX record. This gateway accepts all mail for our domain and accepts relaying mails from our internal server and external staff…
Thor
  • 151
2
votes
3 answers

How SMTP relay process and relay an email to multiple recipients on different domains?

Given an email transaction to multiple recipients on two different domains bar1 and bar2: RCPT TO:a@bar1.com RCPT TO:b@bar1.com RCPT TO:c@bar2.com RCPT TO:d@bar2.com This email is sent to a relay. I wonder how does it relay the email to the 4…
Nicolas Labrot
  • 123
2
votes
0 answers

I need to set-up the blocked machine to relay to the unblocked machine using a different port

I have two Windows Server 2003 machines sitting in a network. Server B has port 25 open and can relay emails to the local network's smtp server. Server A does not have port 25 open. How can I set it up to send emails through another port to the SMTP…
Zain Ally
  • 143
  • 1
  • 4
2
votes
1 answer

TCP Dup ACK, segments lost, retransmission during smtp conversation

A customer is trying to send emails with (smaller and larger) attachments to one of our exchange servers, but get the connection reset after timeout is met. To me, it seems that the sending server does not receive the ACKs, and hence resends,…
3molo
  • 4,350
2
votes
2 answers

SMTP mails being rejected by receiver

I run a custom webshop where my system sends out different notifications. Unfortunately yesterday I started receiving a lot of rejected emails. It's not all emails being rejected, only a specific kind. In the example below I've received a response…
kris
  • 123
2
votes
6 answers

How to centralize my mail?

I get a bunch of mail on about 20 different servers that I'd like to get to one. The boxes are running Linux and right now my solution is to create a TCP relay. I want anytime traffic coming in on port 25 for it to be relayed over to a box somewhere…
tenshihan
2
votes
2 answers

Smtp relay service recommendation to increase deliverability

I need a recommendation for a email relay service to use on multiple domains with C#. I don't want to worry about blacklisting and am looking for increase deliverability on confirmation emails etc. Currently, trialling SocketLabs…
asn1981
  • 61
1
2 3 4 5 6 7