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.

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Internal Address Spoofing using Outlook SMTP Server

Is there a way to harden Exchange Online to prevent spoofing of internal addresses using SMTP? For example, if I connect to Outlook's SMTP server and issue the following commands: HELO domain.com MAIL ...
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Postfix header_checks are ignored

I'm using Ubuntu 20.04. I installed Postfix (v3.4.13) with Dovecot (v2.3.7.2) a long time ago. Now, I want to overwrite the Message-Id header using header_checks. It's the first time I'm trying to use ...
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Windows and Ubuntu on same VLAN, but only Windows connects to telnet smtp.gmail.com 587

I'm having trouble trying to communicate with the port 587 on smtp.gmail.com on Ubuntu only, but the network and firewall teams (FortiGuard, I think), say that this is not a network nor a firewall ...
Cintya 's user avatar
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Postfix - forwarding mail to an external email address

I'm not normally a Linux server guy: I'm a .NET programmer. However, I inherited a situation where there's a website hosted on a Linux server using Postfix on Webmin. They have several aliases set up, ...
SEFL's user avatar
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Exim: send emails from different ips and hostnames on the same vps

I have 2 ips on my server, I’m trying to set up 2 emails, one email sends from one ip, the other sends from the second ip. The first email is fine but I’m getting an error in mail-tester.com for the ...
user2765920's user avatar
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3 answers
473 views

How to avoid reverse DNS errors

I am running a mail server (Exim) on a VPS (Ubuntu 22.04 LTS). I am able to send and receive emails without problem, but I do get the following errors from mxtoolbox.com: Reverse DNS does not contain ...
Bruce Button's user avatar
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2 answers
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Sendmail unable to find recipient to send email

I am trying to set up sendmail for my server to send alert notification status. After searching for guides on the internet, I am still unable to send outgoing emails to my work email. from what I've ...
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Postfix - route mail based on Sender/Connecting IP?

I would like to configure my Postfix mail relay to route mails received from another server on my network to a specific upstream mail server. There are a wide variety of recipient and reply-to ...
motorleague's user avatar
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POSTFIX - sending mails. My mails sent outside bounce back

main.cf compatibility_level = 2 command_directory = /usr/sbin daemon_directory = /usr/lib/postfix/sbin data_directory = /var/lib/postfix mail_owner = postfix myhostname = mail.aufy.pl mydomain = aufy....
aufy's user avatar
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Upgrade SMTP Server on Ubuntu Linux 18.04 to support TLS 1.2

Client has an intranet hosted with Apache on Ubuntu 18.04. When I update an employees information through it, an email is sent, but it fails showing the following error: (SMTP Error: 421 4.7.66 TLS 1....
Nico Nico Pizza's user avatar
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How to set up a postfix relay server for Google Workspace(gmail)?

There is a need to make a relay server for the company's corporate mail. The need arose due to the presence of some google ip in the spam lists, and this sometimes leads to the fact that letters end ...
Tarik's user avatar
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Not receiving any response from SMTP server after successfully connected via openssl or telnet

I am trying to set up my postfix using Gmail smtp relay server. I have set it up in other servers without issues, but I am having difficulty getting it to work in my work network. I tested if there is ...
ricardo3889's user avatar
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1 answer
515 views

What could be causing PowerMTA not to forward emails over port 465 SSL...?

We have a PowerMTA server that receives incoming e-mail. and forward it to external SMTP server that's not running PowerMTA i tried to do it using port 587 and port 25 both working fine and emails ...
Sabrina sage's user avatar
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SMTP Relay - Keep sender SPF valid

We use a email setup (incoming mails) in the following order: Internet -> on premises mailserver (=> attachment filter, antivirus, spam filter) -> forward to Microsoft 365 Exchange Online ...
Robin Reuter's user avatar
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Postfix - Relay - authentificatin in Mysql

I tryed to manage with a postfix server, my goal is that : When 1 special user ([email protected]) try to send mail, it will use routing (using a relay server is OK) but I don't understand how to send ...
PopFR1's user avatar
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Redirect OR warn (during initial negotiation) SMTP submitters to use TLS on port 587 - leave 25 explicitly blocked by firewall for better security [closed]

I've managed to find a lot of closely related information, but not an answer truly addressing my question. I am expanding on my homelab server, and have decided to use a small publicly hosted server ...
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Best Practice - SMTP Time Out

Good Day, The question is quite straight forward. What should be a best practice to time out a SMTP connection on the RECEIVING side? Background: We are currently having an issue with a sender that ...
pSyToR's user avatar
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Postfix to gmail relay - preserving the sender's address

Relayed emails come 'from' [email protected], not [email protected], so I cannot reply. I have several domains and am using Postfix to relay emails sent to [email protected] on to [email protected] as ...
Megalomatt's user avatar
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how to switch from outgoing port 25 to 587 in postfix

I would like to send a mail to a gmail address: echo "This is the body of the email" | mail -s "This is the subject line" [email protected] That is what I see in the logs connect to ...
laplasz's user avatar
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SASL Authentication - Why is it taking so long to login to the authentication server?

I can't describe it properly, but I have a Thunderbird mail client, I use it to receive and send mail through a user I created and an available domain. I use IMAP and POP3 services there, I also have ...
Pasrdfffsas's user avatar
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iptables - port 25 not getting traffic even though default policy is ACCEPT and all rules are flushed

I am having a problem that's driving me up the wall. I have a server, where after several attempts at various iptable rules, I have flushed iptable rules and set default policy to accept. The output ...
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Exim allow outgoing for specific domains

I am using Exim as MTA. I want if an email is sent out from my server, then the sender domain must be in the list "+local_domains", else it should be through the message "Not Allowed&...
Rahul Mukati's user avatar
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Dell IDrac8 SMTP setup diagnosis - RAC0225

I tried to setup the mail warnings on an IDrac8, it's not my first time, that's why I am wondering what I am doing wrong. on this server it won't send mails with following error "RAC0225 sending ...
homeFault's user avatar
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1 answer
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Postfix/Dovecot - Initial Config - Test Email Results - 554 5.7.1 Client host rejected: Access denied

I sent an email successfully. Can't say the same for receiving. When I attempt to, I get an email saying that the message was blocked with the following diagnostic code: Diagnostic-Code: smtp; 554 5.7....
Anthony Mallgren's user avatar
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576 views

Configuring Google Workspace (Gmail) to trust a Mail Relay via ARC?

I am building a system which modifies incoming emails body on the fly (for example, it deletes attachements with viruses). Of course, I break the DKIM signature when there is one. Is it possible to ...
user37220's user avatar
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opendkim-testkey: key not secure (file permissions are good and TrustAnchorFile config setting is set)

If I run sudo opendkim-testkey -d mydomain.com -s selector -vvv, I get opendkim-testkey: using default configfile /etc/opendkim.conf opendkim-testkey: checking key 'selector._domainkey.mydomain.com' ...
Robert K S's user avatar
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1 answer
758 views

Exchange Server 2019 can't send email on port 25

I have setup a windows server 2022 with Exchange 2019 and am unable to send out email because outgoing port 25 is blocked. Vultr.com says they have removed the default SMTP block from my barebones ...
Craig deepC's user avatar
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Why exim does not use TLS when sends email to remote SMTP?

Here what exim does when sends emails to gmail and other SMTP severs Received: from ns01.virtex.kz (ns1.virtex.kz. [185.141.164.16]) by mx.google.com with ESMTP id i11-...
Falseclock's user avatar
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What exactly is Return-Path and who sets it?

This article (https://www.sparkpost.com/resources/email-explained/return-path-explained/) explains "Return-Path" as follows: When an email doesn’t make it to its intended destination, the ...
Myzel394's user avatar
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Gmail not detecting PTR record from vultr server

I have an SMTP server running on a vultr VM. I've set up the rDNS to point to my mail domain name mail.idimitrov.dev. The DNS setup points to that machine on ipv4 and ipv6 for mail.idimitrov.dev and ...
Ivan Dimitrov's user avatar
1 vote
1 answer
538 views

Postfix white listing a badly configured server not working: Helo command rejected: Host not found;

My mail server configuration is rather strict and some times incoming mails from legit servers get rejected because the remote end has a configuration problem, a common one is the HELO hostname. I ...
moray's user avatar
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Configuring postfix to use SendGrid SMTP relay with fixed FROM address but need to append REPLY-TO of original sender

I have been trying to resolve for a couple of months using multiple different configurations. The local delivery to a Dovecot mailbox ([email protected]) keeps the original sender (sender@gmail....
kcfez's user avatar
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1 answer
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AD lockout email alert script working intermittently

So we've been using this PS script for a while and was working fine until we migrated the domain controllers. The new domain controllers are running core Microsoft Windows Server 2019 Datacenter. We ...
imaxt's user avatar
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2 votes
2 answers
620 views

Slow SMTP responses with Exchange 2013 (Not network infra related)

(I know 2013 is shortly out of support, and it will be replaced, but in the interim, I'm experiencing an issue I would like to fix.) I will use telnet over port 25 as my example, but normal traffic ...
wnogt's user avatar
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1 answer
971 views

Nginx mail proxy: tls between the proxy and the server?

When using the Nginx Mail Proxy feature to realize an SMTP proxy, there are several options available to configure (start)tls between the client and the proxy. However, it appears between the proxy ...
Arnout Engelen's user avatar
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819 views

Haproxy will not load balance smtp

I have been struggling with Haproxy for a long time now to configure smtp load balancing. Whatever I do, the server responds with a black screen and no possibility to try out smtp commands to test. ...
02dag's user avatar
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Mailgun Suppression List functionality

Running a mailman list on Redhat using Postfix. Trying to understand a couple of closely related concepts about Mailgun's Suppression List or Bounce List. Is it "permanent", in the sense ...
Sam's user avatar
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1 answer
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mx record with IPv6 AAAA host

I need to setup a mail server or mx record with a IPv6 address I have written a AAAA record which is working fine (pings, ports) here I have setup hmailserver and checked all ports(587, 143) with ...
Pradyut Bhattacharya's user avatar
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1 answer
134 views

How to improve sender score for personal mail server

Background: I have an own domain and an own mail server that sends out the mail for this domain. The users are only my family so there are less than 10 users with probably 20 mails sent per day. ...
Tode's user avatar
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1 vote
1 answer
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Email proxy architecture

I'm trying to figure out how email proxies generally work. I want to present the way I see the architecture, would be glad if anyone could explain which of my assumptions is flawed and what am I ...
Evgeny's user avatar
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2 answers
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Root domain in SPF record instead of full hostname

Can i use root domain like google.com instead of _spf.google.com in SPF record?. My SPF record v=spf1 include:_spf.mx.cloudflare.net include:_spf.google.com include:mxsmtp.sendpulse.com +a +mx ~all ...
Stellan Coder's user avatar
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610 views

Whitelisting Gmail SMTP in CSF

In my csf.deny, I have 0.0.0.0/0 blocked to prevent requests being sent to the raw server IP. This creates issues with sending e-mails. I utilize Google SMTP to send e-mail. I can't seem to figure out ...
anxiety's user avatar
5 votes
2 answers
2k views

Generate DKIM for Gmail Free Account

I am using Gmail SMTP with wordpress to send mail with my custom domain ([email protected]). Emails are successfully sent but always land in spam folder in every webmail provider (Eg, Gmail, Rediffmail,...
Mehul Kumar's user avatar
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1 answer
105 views

Postfix: different smarthosts per server port

I need to install Postfix and let it listen on two different ports: 1025 and 1026: /etc/postfix/master.cf: 1025 inet n - y - - smtpd 1026 inet n - ...
Mat's user avatar
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Client is sending SMTP emails but they are not recorded in the "Sent" folder in webclients

I have been using instantly.ai to send emails. I connected IONOS.ca and JustHost.com mailboxes to instantly and it works fine (warmup, receiving and sending [yes other emails receive the emails sent, ...
Guest Man's user avatar
1 vote
1 answer
7k views

Postfix "Client host rejected: Access denied" how to diagnose the precise reason?

I see this question asked over and over on serverfault, and each time it seems to accompanied by a copy of the configs and result sin a successful or not diagnosis by wonderfully helpful readers. I ...
Bernd Wechner's user avatar
-1 votes
1 answer
1k views

Possible to host own SMTP server without port 25 open

I have a VPS on Digitalocean and Hetzner, but both block port 25, so I cannot host my own SMTP server here. However port 587 is open, so my question is: Is it possible to host your own standalone SMTP ...
Andreas Andersen's user avatar
-2 votes
2 answers
1k views

Inetmgr6.exe missing on Windows server 2022, SMTP relay still working

4 months ago, I have in-place upgraded a 2K8R2 server to 2K22. It had the SMTP relay function, and this feature is still working on Server 2022. (I did the export-import function to get the settings ...
Fragobar's user avatar
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1 answer
342 views

exim4: how to add an address as BCC to all the outgoing emails?

I'm working on an Ubuntu 20.04 web server where exim4 is used to send emails from the PHP application running on it. Due to diagnostic and archival needs, I need to configure exim4 to automatically ...
Dr. Gianluigi Zane Zanettini's user avatar
1 vote
1 answer
302 views

I setup DMARC p=reject on server but now I can't send via gmail to gmail (using server email From address)

Did I shoot myself in the foot ? I mainly use gmail to send and receive emails. Support etc. My default 'send email as' profile is not the gmail address itself but an address on my server (also the ...
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