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

3133 questions
1
vote
0 answers

Office 365: 'client smtp submission' suddenly starts failing. How to diagnose client auth error?

Since a few days, my application fails sending SMTP email. The app is in fact a scheduled task (which is running on my local machine, written in C#, using SmtpClient) and occasionally needs to send one (or a few) emails. The code is similar to…
jeroenh
  • 111
  • 4
1
vote
2 answers

Correct FQDN Setting?

I can see from SMTP logs that some mail is being rejected OutboundConnectionResponse SMTPSVC1 Sxxx - 25 - - 504+:+Helo+command+rejected:+need+fully-qualified+hostname 0 0 69 0 47 SMTP In IIS6 > SMTP > Delivery > Advanced I can see that the…
Neil Thompson
  • 125
  • 1
  • 7
1
vote
1 answer

Where does e-mail header "Received: from..." come from?

I sent myself an e-mail from my server to my gmail account, here is one of the headers (partially redacted): Received: from cpvds3xx.xxx.com (dev1.xxx.com. [209.51.132.xxx]) by mx.google.com with ESMTPS id…
THX-1138
  • 121
  • 4
1
vote
1 answer

hMail delivery queue full with unsuccesfull spam

Since a day or two the mail delivery queue of the hMailServer is exploding because someone is trying to send spam via this server. Though the e-mails aren't successfully sent it fills up the mail queue. All SMTP connections require smtp-connections…
Sebass van Boxel
  • 63
  • 1
  • 7
1
vote
1 answer

Is extra "Received by" in mail headers bad and can I remove it?

I use our own VPS web and mail server to send out a newsletter regularly to 50,000 addresses. I am trying to improve deliverability and was looking through some of the thousands of bounce emails. One thing I noticed was that there is kind of an…
johna
  • 121
  • 1
  • 3
1
vote
3 answers

Backscatter Issue

Can somebody please help me with this issue. In our company we are having issues sending emails to @hotmail.com addresses. I have contacted Microsoft "Support" directly about this issue and they suggested getting our Domain hoster to publish a SPF…
The Woo
  • 579
  • 6
  • 21
  • 39
1
vote
1 answer

Send email through Gmail SMTP to avoid local delivery attempts?

Background We use Google Apps for email with our domain example.com: [ec2-user@example ~]$ dig MX example.com … ;; ANSWER SECTION: example.com. 300 IN MX 1 aspmx.l.google.com. example.com. 300 IN MX …
feklee
  • 505
  • 5
  • 19
1
vote
1 answer

Restrict SMTP for localhost only

How can we restrict SMTP service to be used on localhost only? Our websites are using localhost SMTP but we do not want any mail clients to use our server on SMTP port. Our server is Windows Server 2008 R2 and using Mail Enabled Professional Edition…
Jonas T
  • 225
  • 3
  • 9
1
vote
1 answer

What are the security risks with running an SMTP server?

I'm running Windows Server 2012 and I would like to set up an SMTP server to work with my hosted websites. I've previously installed various roles on my server which have resulted in exposing security holes. Since then I have tried being extremely…
JSideris
  • 313
  • 1
  • 3
  • 8
1
vote
3 answers

How to make postfix send email when fail delivery attempt?

i'm setting up postfix as a MX server. Basically it will receive email, do all filterings and route to domain SMTP server. In case of failure when trying to send the email to the destination SMTP, is it possible for postfix to send email to the…
Abi Aqil
  • 53
  • 1
  • 5
1
vote
1 answer

SMTP as SmartHost for SendMail

My general task is following: We have workable application that sends mails to the users (that are registered in this application on some actions); Mails are sending using sendmail tool; In order to test changes our sendmail tool uses smart host.…
fashuser
  • 123
  • 5
1
vote
1 answer

Using mime_header_checks to ACCEPT instead of REJECT?

I'm pretty well versed in using header_checks/mime_header_checks to refuse smtp mail in Postfix, but now I think I've gone off the path of righteousness; I'm trying to suss out a way that I can refuse a message if it doesn't contain one of the…
GeminiDomino
  • 121
  • 5
1
vote
0 answers

Outlook on Exchange: Why does it mangle return address for some email?

We have seen this too much in multiple Exchange environments, and need some guidance. When we email (using simple mail client app) to certain Exchange/Outlook sites, when those sites hit Reply, our email address is mangled, resulting in the reply…
Jonesome Reinstate Monica
  • 5,445
  • 10
  • 56
  • 82
1
vote
1 answer

McAfee Secure Messaging Service / Postini: false positive?

I'm puzzled by this email message that gets quarantined by McAfee Secure Messaging Service (it's based on Postini) for no reason that I can think of. Here are the Postini headers: X-pstn-2strike: clear X-pstn-neptune: 0/0/0.00/0 X-pstn-levels: …
Martin Schapendonk
  • 131
  • 4
1
vote
1 answer

Sendmail dropping domain name from the username

I'm setting up Dovecot with Sendmail and I almost have it working (I think). The username for the account is a full email address such as "username@domain.com". What seems to be happening is that when the username is passed over to dovecot-lda from…
Nick
  • 11
  • 2
1 2 3
…
99 100