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.

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What is “mail._domainkey” and why would it be a DNS “TXT” record with a string “k=rsa; p=[base64]”?

I added some new IP addresses and domains to a VPS (Centos) managed with Vesta Control Panel. Everything seemed to work, but then, a few hours later, I noticed some emails (SMTP) from a previous, ...
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22 views

deny an email from sender at one of my mx records, so it tries the other mx record

Does anyone know what SMTP reply code I can give to a sender trying to deliver mail to my server so it knows the mail can not be delivered to my server. But not a hard fail so it bounces the email ...
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54 views

Is it possible to modify sender address if I use Windows Server 2012 R2 as SMTP relay?

I am working in a company that only allows email address on the directory to be sent. But for HP iLO alertmail system, it does not allow users to modify the sender address. The sender address is ...
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2answers
67 views

Internet facing Hub Transport Exchange server with Internet restricted users and a Canon Copier

This is a rather convoluted problem but I hope that someone out there has experienced a similar situation. Here are the facts of what is happening: We have a single Exchange 2010 server that is ...
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41 views

How to pass email from intranet hMailServer to Internet server

I have had hMailServer running on an intranet in an industrial application for years without trouble. It accepts email reports from machines and parses them into an SQL database. I now wish to send a ...
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410 views

Outlook.com rejects: 550 SC-001 (BAY004-MC5F13)

I am operating a cluster of 3 dedicated machines for a webapp, each of those uses sendmail as MTA. Hostnames are node1.domain.com node2.domain.com node3.domain.com Unfortunatelly outlook.com rejects ...
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1answer
97 views

Cannot set a default SMTP server certificate on Exchange Server 2013

I've an Exchange 2013 Server with two wildcard certificates, one for matching the internal AD zone and the other one with the public domain. The certificates are defined with those names: *.example....
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1answer
60 views

SMTP not reachable

for some time now I am not able to reach SMTP on port 25 or 587 on a server of mine from the outside though both ports are open and postfix is listening on them: $ telnet domain.tld 25 Telnet escape ...
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19 views

Relaying for SMTP Virtual Server

On an external server I installed the SMTP Virtual server using this how to: http://www.lukepuplett.com/2010/06/how-to-send-email-from-microsoft-server.html I setup the firewall so localhost and the ...
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3answers
106 views

How can I find out which script/program/user invokes exim (and is sending spam)?

The problem A client of mine asked me to take a look at his shared-hosting webserver for the following problem, but I'm stuck at finding out what's wrong. His server is being blacklisted by a lot of ...
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72 views

How to pass through credentials in SMTP proxy with Postfix

I want Postfix to proxy SMTP connections from MUA on my client to another outer SMTP server. Since the outer SMTP server requires the Postfix proxy to authenticate with SMTP-AUTH, So I set my MUA's ...
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53 views

iRedAdmin SMTP sending error

Recently i installed iredadmin on Debian. Then i tried to send mail using laravel framework with SMTP settings, but i cant get the email. This is my mail error log: Nov 26 10:19:43 server ...
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1answer
217 views

“SASL authentication failed” when authenticating to receiving mail server

Some recipients do not receive emails from my Postfix 2.11.0 server. Their servers reject my SASL connections with errors like 535 5.7.8 Error: authentication failed: authentication failure and 535 5....
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1answer
91 views

Users allowed to send mail using postfix

I've installed postfix and opendkim on my ubuntu server, intending to use this server as a private relay for an application to send "activation" emails to new users. I configured SASL authentication ...
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1answer
119 views

sending emails fails with gmail only

My debian server sends email to yahoo, hotmail but not to gmail ! tail /etc/log/mail.log 95.211.117.206], dsn=4.0.0, stat=Deferred: Connection timed out with 75gmail.com. Nov 23 23:07:52 sitechat ...
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2answers
132 views

exim4 keeps retrying message that fails after “closed connection in response to sending data block”

Let me start by saying that I'm not an IT guy, but I've been pressed into it in my office. Someone at my office sent an 86MB e-mail attachment to someone at aol.com, and aol.com is rejecting the e-...
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48 views

sendEmail dh key too small

We use sendEmail to interface to customers mail server and send e-mails out of our software. currently I am attempting to authenticate send email against an ATT e-mail account. I keep getting the ...
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13 views

Are there issues in whitelabling a SMTP server (not mine) with an A record that doesn't match 200 helo?

I know that a CNAME and a MX record can't exist on the same host. In this scenario I'm using A records to manage SMTP for 350 DNS domains. companyA.com MX myAlias.whitelabel.com companyb.com MX ...
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Is reverse DNS a good method for promoting grey IPs from trusted domains to white?

I'm trying to set up a mail server using OpenBSD, OpenSMTPD, spamd, and pf. The first problem I've encountered is that many large webmail providers - like Gmail - will retry delivery from a different ...
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1answer
312 views

SMTP HELO command from Windows gives 500 Command unrecognized error, same command from Linux returns Hello

We have a Java web application that needs to send out emails to our users, and I'm getting this Java error when those emails try to go out: javax.mail.MessagingException: Could not connect to SMTP ...
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2answers
69 views

Is it a good idea to reduce the give-up time for e-mail delivery?

We run an e-mail server for a few customers, and we've recently run into a bit of a conundrum. We had a user who sent an e-mail to an incorrect e-mail address. The incorrectly specified domain ...
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122 views

Using postfix to send email in redmine

I'm trying to configure sendmail to send emails from the Redmine installation (which I still haven't figured out how to run with Apache). When I send mails from the terminal, with the command (example)...
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2answers
156 views

How can I use wildcards for sendmail TLS_Rcpt?

sendmail lets one place restrictions on TLS conversations. I want to check that messages sent to example.com are sent to a server that has a *.messagelabs.com certificate. I want to protect against ...
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61 views

Postfix permit localhost use plain login

I have postfix 2.11 setup on Debian jessie with Dovecot SASL and I require encrypted login mechanism to send mail via smtp. For this purpose in the main.cf I've smtpd_tls_auth_only = yes option set. I'...
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1answer
159 views

Gmail accepting postfix relay via Port 25 but rejecting emails sent via TLS login on same server?

I have a postfix email server that handles mail via two routes. First is a relay on port 25, this is dedicated to a single external IP address via a 'mynetworks' entry. This route is to handle email ...
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46 views

Email validation fails on HELO / RCPT TO commands to records

I'm migrating a mailing service from a server to another. Before setting up new mailing list I wanted to process it through an email validtor I've setting up on the server. I basically used this tool ...
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61 views

Exchange 2013 SP1 on WIndows 2012 R2 SMTP Issue

I have Exchange Server 2013 SP1 installed on Windows 2012 R2. This is a clean install on a new stand alone server. I have added 1 user account into Active Directory and have the receive connectors ...
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1answer
1k views

Graylog failing to send emails (SMTP)

i am trying to let greylog2 send me email alters but i am getting this error no matter what i try? i am trying to use smtp.gmail.com as email server. This is the error message i am getting The ...
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2answers
239 views

What exactly does “stat=Deferred: Connection refused by [x.x.x.x]” mean in sendmail logs?

Can someone please clarify what exactly a sendmail log entry for stat=Deferred: Connection refused by [x.x.x.x] means? At what point in the SMTP conversation can/will sendmail throw this error? ...
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256 views

Recipient address rejected: User unknown in virtual mailbox table

I have a dedicated linux server running Plesk 12.0.18. On this server, I have running 61 subscriptions, only 1 have this problem. When I want to send an e-mail using roundcube from 1 of my ...
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1answer
152 views

Exim error SMTP call from [X.X.X.X]:50135 dropped: too many syntax or protocol error

My clients server access keeps getting blocked by CSF. The Exim log produces: no host name found for IP address X.X.X.X Exim error SMTP call from [X.X.X.X]:50135 dropped: too many syntax or ...
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1answer
126 views

Very slow smtp server response

I recently have created a server on https://www.scaleway.com/. Server's OS is Fedora22. I installed a SMTP server (postfix). It works fine, but I have very slow response from it. Any message, that I ...
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51 views

Email connection timeouts and Barracuda

I am running into an issue with Barracuda's new cloud-based Email Security Service (ESS) that several partner companies have switched to recently. We are unable to email any domain behind the ESS ...
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36 views

mailx is working to send mails to external network. But mutt is not working?

I have a server with postfix service running. I am able to send mails to external network using mailx. But with mutt, I can only send mails to users inside network. What I might be the issue? ...
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335 views

SMTP connection from closed by QUIT

2015-10-21 08:54:02 H=zeus.email-sent.net [66.241.99.248]:2594 Warning: Sender rate 1.0 / 1h 2015-10-21 08:54:02 H=zeus.email-sent.net [66.241.99.248]:26166 Warning: Sender rate 2.0 / 1h 2015-10-21 08:...
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1answer
81 views

Why does sendmail changes the FROM domain and how to configure the proper one?

I installed Jenkins and configured it to send emails as being sent from "jenkins@jenkins.example.com" but the address is always changed when email is being sent and I receive the mail as being sent ...
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SMTP slowness on Ubuntu

I'm using a Linux client machine, connecting to a 3rd party external mail server. The mail server takes extremely long to respond when I try sending mail. To debug this, I installed the mailx basic ...
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3answers
238 views

Dovecot/postfix: forward all current messages

What I'm try to achieve it's pretty simple, and, after googling, its hard to believe I've been unable to find a solution. What I want is to forward all current messages (already delivered) of an user ...
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1answer
222 views

Setup Postfix with SMTP-AUTH over SASL2 with SASLDB for users to send emails

Hello, I spent the last few days trying to setup Postfix with SASLDB to send emails from my application over SMTP on Ubuntu Server 15.04. I searched, read and tested a lot about it but I can't get it ...
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2answers
81 views

Postfix, carbon copy forwarded email

Basically this is the setup I am currently using: virtual_alias_maps x1 x2 recipient_bcc_maps x2 x3 When I send an e-mail to x1, I expect it to be forwarded to x2, and then copied to x3, but ...
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2answers
104 views

postfix dsn=2.5.0 won't send notification

I'm facing a problem with Postfix. I've configured it to send notifications if message delivered, bounced, deferred. I recieve notifications, but some times in logs I get record like this: 1765BA8A0: ...
14
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1answer
2k views

Security risk of POP before SMTP

I received an email from one of our servers this morning (CentOS, with WHM running LAMP) stating: The server has POP3 before SMTP enabled. For security reasons, cPanel highly recommends that ...
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1answer
83 views

Why nmap result is different from online port scanner result?

I have a vps A, and I am running smtp on it. If I run nmap from my local desktop to scan for my vps it turns out that port 25 (smtp) is filtered. However, if I run online scanner (fill my vps's IP ...
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Forward email for ONE user to another SMTP server [duplicate]

I have a postfix server that takes email for example.com and uses an alias table to redirect mail to several personal gmail accounts. Recently we were asked to test a new email provider. This email ...
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1answer
93 views

Restrictions for postfix submission port

I would like to set up Postfix (on ubuntu 14.04) to use the submission port but I'm worried It may become an open relay. I would like to know what are the best restrictions for each of the ...
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Postfix mailserver only allows sending from ONE email(support@domain.tdl), and only THAT email for THAT domain, but receiving from outside is fine

As the title says, I can only send emails(through webmin + thunderbird) using the support@maindomain.de email, but using other domains/accounts like blah@maindomain.de, wont send it(even though webmin ...
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1answer
106 views

How to Stop Exchange Server 2003 sending out Mass Spam / Virus Email from Unkown Account?

I'm young and new to the scene, I have been working on a family member's business server. It is an old server and has a few problems but has a big main one I'm trying to fix now. I'll try be as clean ...
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1answer
55 views

postfix smtp remote - connection timedout

I have an ubuntu server installed on a remote server on amazon. I'm trying to allow remote connections to send email per user/password that is configured by the ubuntu system. means each user in my ...
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1answer
145 views

Mail send by server gets denied by mx.hotmail.com [duplicate]

I got an notice that some clients werent receiving their emails, all clients used hotmail accounts, while i looked into logs i got this part Sep 25 07:52:51 s22090 named[25045]: client 127.0.0.1#...
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417 views

Exim not always sending AUTH LOGIN username/password

We are sending mail using exim (configured through WHM). With the same exact configuration, seemingly most of the time exim sends the correct AUTH LOGIN username and password, however sometimes it is ...