Questions tagged [smtp]

Simple Mail Transfer Protocol. A protocol for delivering e-mail from an end user to a server for storage and later retrieval by the intended recipient.

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48 views

No MX Records on a Possible Phishing domain?

I saw on my SMTP logs that it queried a possible phishing domain, I look up on its MX records and it didn't have one. Does the domain need an MX record before sending phishing emails?
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Does user need to keep updated with the certificates locally when using TLS with smtp?

https://wjianz.wordpress.com/2014/09/03/howto-installconfigure-msmtp-and-mutt-on-ubuntu/ I got GTS CA 1O1 as the common name instead of Google Internet Authority G2. What is the difference between ...
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Spoofed email: can't determine Purported Responsible Address

I am studying the SMTP protocol and follow a course materials to setup a PoC spoofed email by talking with a SMTP server of our department. This is what I have right now: shuaiw@shuaicpu1:~$ telnet ...
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11k views

How do email clients “send later” without storing a password?

Email clients like Spark for macOS have a feature where a user can send an email later, at any given time, even when the computer is turned off. An SMTP server needs a password based authentication, ...
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TLS 1.0 Deprecation and Mitigation Tactics

With the deprecation of TLS 1.0 on the horizon, I'm curious how others are handling connectivity and mail delivery issues for dated client environments. Lets face it, there are more environments live ...
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Weird character sequence in email subject

I've noticed that the subject in one of the spam emails looks like this in source: Subject: Offe=?UTF-8?Q?=EF=BB=BF?=r fr=?UTF-8?Q?=EF=BB=BF?=om C=?UTF-8?Q?=EF=BB=BF?=redi=?UTF-8?Q?=EF=BB=BF?=t On=?...
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Suspicious SMTP server client activity - non-ASCII queries

I've noticed some strange activities from some remote host connected to our SMTP mail server. Queries contains non-ASCII characters, below is the copy of one of them (to each query our server ...
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66 views

Block SMTP Connection That Doesn't Have Credentials

I am able to do the following and connect successfully without any type of credentials: telnet <IP Address> 25 When I am in I can verfiy emails, send emails, etc. I feel like this is a ...
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Postfix SMTP - Can I use SSH public keys instead of sasl password

I am relatively new to managing mail server, although i am familiar with webhosting servers not running dedicated email services. Postfix is configured to use sasl-password authentication I have ...
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983 views

How to test if TLS is enforced for emails sent through SMTP? [closed]

We are planning to create a rule in Proofpoint to enforce TLS on all outgoing email. I need to test that the rule is working and emails are bouncing if the recipient SMTP server does not support TLS. ...
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225 views

How to extract intresting data from malicious e-mail header

Premise: I know pretty well how SMTP works, and how to read an e-mail header. I know what all the main fieds mean, but I couldn't know what to look for if I want to know if the mail is kind of ...
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What are recommendations for unblocking outbound SMTP traffic in an organization?

Our organization has blocked all outbound SMTP traffic under the assumption that we are preventing potential botnet spamming issues which lead to blacklisted IPs. However, I've seen other ...
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1k views

Is there a list of open mail relays I can use for a pentest? [closed]

I'm currently pentesing a client (with permission of course) and we are testing their email filtering capabilities. We want to check whether they reject mail coming from open mail relays, but I seem ...
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81 views

Database in DMZ and SMTP relay

I have an application that talks with a database in the DMZ. There is a firewall between the apps and the db but our developer thought that they require a mail notification that is triggered from the ...
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184 views

Why would an attacker try SMTP login many times even though it is disabled?

I recently set up an SMTP server for myself to use, and I am getting some traffic from two IP addresses and none else (though for obvious reasons I will not state the addresses here). An example ...
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Simple Mail Delivery Protocol (SMDP), where is it today? what do you think of it?

So I'm doing a research study on Simple Mail Delivery Protocol (SMDP) for those of you who don't know what it is, it's a new protocol for Email delivery that promises complete anti-spam filtering. ...
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65 views

Running open relay smtp in company network

We are producing IoT gateways which send out emails via SMTP protocol for user notifications. These IoT gateways are mainly used by corporate customers in intranets without access to or from the ...
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Domain offline - are unmaintained email clients a security risk?

I have just unregistered a domain. Now my mail client (Thunderbird) popped up a message saying that it cannot connect to the mail server. That's fine - for the moment. However, I wonder what would ...
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471 views

SMTP Service STARTTLS Plaintext Command Injection

We are getting this vulnerability on SUSE Linux Enterprise Server 11. This vulnerability is getting triggered on port 587 for postfix. I have checked several links but I am unable to get any relevant ...
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Why is hotmail mail server providing an invalid certificate?

It seems that hotmail.com mail server sitting at hotmail-com.olc.protection.outlook.com is using a TLS certificate issued to mail.protection.outlook.com. Both the mail server hostname and TLS ...
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158 views

Can password be stolen when doing SSL/TLS-protected IMAP/SMTP in public network

My email password has been stolen most probably while I was on vacation in another country and was using hotel's (and maybe others, cannot remember) WiFi networks to read and optionally send emails ...
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1answer
81 views

Why doesn't SMTP check that users are authenticated to send from an address?

I think it's a bit different from this question since it's about SMTP, but similar idea. Wikipedia says on email spoofing: MAIL FROM: - generally presented to the recipient as the Return-path: ...
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721 views

Close Port 587 - Ramifications?

Our recent PCI scan failed because "Plaintext authentication is allowed over unencrypted channel on SMTP." As such, our tech support suggested to close port 587. What are the effects of closing port ...
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491 views

How to securely store user-specific mail server credentials at the server side of a web application

I have an asp.net web app that generates emails when users perfrorm actions...these emails are generally notifications to other users that they should see/do something. The users can be internal to ...
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173 views

How secure is e-mail landscape right now?

In light of recent news about some flaws in PGP standard, I (a non-PGP user) started to think how secure are regular e-mails these days. I have found the STARTTLS Everywhere project, and they have a ...
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311 views

Can SPF be bypassed by using a shared email server?

As I understand it, SPF works by listing permitted SMTP server domains in the TXT DNS record of the domain you own. So if I own example.com and wish to permit a 3rd-party SMTP server at smtpexample....
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489 views

Is it possible to disable SSL over SMTP/POP to the mail server that enables SSL/TLS?

I'm using thunderbird where I can check the option whether I will use SSL/TLS or not. However in my company's server, SSL/TLS is enabled both on POP3 and SMTP. Is it possible to disable SSL/TLS on ...
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59 views

SMTU AUTH and compromised user

Recently I've set up two SMTP auth-enabled sendmails, and within a week and month both of them were used to send unsolicited mail using SMTP AUTH. Attackers were acting from different IP and using ...
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1k views

How to get the IP Adress of an email receiver

I am communicating through email with a scammer who is trying to by me mw own parcel of land. I already contacted the police but it could take 2 to 3 months before they start investigating. I want to ...
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388 views

SSL/TLS compression attacks on mail servers (smtp)

Currently, we know few compression attacks on the SSL/TLS protocol (such as Crime or Breach). I wonder for few days if these attacks are practicable on a mail server (smtp). Is CRIME attack ...
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516 views

Why did PHP 5.6 change how it handles SSL certificates?

I was using PHPMailer to send an email with SMTP. This time I used PHP 5.6. I received the following error. Warning: stream_socket_enable_crypto(): Peer certificate CN=`*.example1.com' did not match ...
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634 views

Why are common services using implicit SSL not considered obsolete in the way that SMTPS is?

SMTPS (implicit SSL) has been deprecated/obsolete since SMTP+STARTTLS (explicit SSL) was defined in RFC2487. I'm not entirely clear on the reasoning behind that, but it was clearly considered a good ...
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1k views

What happens if STARTTLS dropped in SMTP?

SMTP uses STARTTLS extension to upgrade SMTP to SMTP Secure (STMPS). According the the RFC, the client and server starts TLS as follows: S: <waits for connection on TCP port 25> C: <opens ...
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9k views

How a spoofing email site such as emkei works

I'm trying to understand how email spoofing works. After studying the technical process, I have finally understood that : 1)The spoofer will try to scan every ports of a smtp server to catch the mx ...
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855 views

Email Security Gateway vs Firewall [closed]

An email security gateway is an edge device such a router that serves for relaying the external network with the private network. It helps with detecting and blocking spams and phishing emails. That ...
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1k views

Is Open Port 25 on Web Server dangerous?

Port 25 of a web server is open. We dont have any email server, since we use google mail server, but still port 25 is open. Is it dangerous to keep it open? If it can be attacked then how it can be ...
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I want to know if exist a vulnerability in using sp_send_dbmail of SQL Server?

I'm using the next stored procedure sp_send_dbmail in SQL Server 2012, the DBA ask me if it possible make SQL Injection using this SP, or SMTP Injection? In the configuration of the Database ...
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16k views

Why does Gmail (add accounts) using SMTP server recommend SSL instead of TLS?

I stumbled something interesting today when I was adding an account to my gmail one. Why is SSL boldly stated as recommended when TLS supersedes SSL? The links for SSL and TLS is the same: https://...
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What security settings is Yahoo Mail looking for to consider IMAP client secure?

When setting up an IMAP client for Yahoo Mail, Yahoo requires the "Allow apps that use less secure signin" option to be enabled. The client is configured to use SSL for IMAP (and SMTP). What ...
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174 views

How to detect SMTP proxy on public wifi?

For a small research project I want to collect characteristics of public wifi hotspots. One topic that came up was SMTP proxy - is there a way to detect a proxy or could I just check whether the ...
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42 views

When is it appropriate to check the from part of a mail address and to not only validate the domain?

SMTP authentication Mailing in same domain This question is based on the answers provided above. The question is not how and why to authenticate server mails from same domain which makes it ...
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731 views

Why is still so easy to send phishing emails?

When I first started playing around with how SMTP worked over 20 years ago, I remember being somewhat surprised how easy it was to make an email appear in someone else's mailbox that looked like it ...
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7k views

SMTP Email Spoofing

While testing my SMTP server using a telnet session from home, I was able to generate an email using the following commands: telnet MyEmailServer 25 HELO MyEmailServer MAIL FROM: ...
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simple question about smtp server ( msa to mta ) security design?

Not sure if this is due to security; hence the reason i am asking here. I have 2 SMTP server and a couple of unix servers the actual mailserver running on window. client connect to it and download ...
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792 views

How to spoof a MIME-level email address

As a sysadmin, I need to send spoofed emails to ensure that the spoofing protection (DMARC, etc) is working. I think Emkei's Fake Mailer can be used to send emails spoofed at the SMTP / 5321.MailFrom ...
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VPS outbound emails security

I have an instance of VPS running with logrotate that emails me logs every day. It is a send-only SMTP server with Postfix, set up using this guide. I just need to receive the logs from this server. ...
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112 views

Using port port 25 on the same WiFi

Me and my brother live in the same apartment and use the same internet connection. (A WiFi router with WPA2 password). He uses Microsoft Outlook as his primary email tool and I noticed that his POP ...
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1k views

smtp port 25 connect failed

If I take any host from https://www.arclab.com/en/kb/email/list-of-smtp-and-pop3-servers-mailserver-list.html why I'm not able to telnet to any of the specified ports ? I'm getting: "Connecting To ...
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What are the security issues of having all services (web, smtp, dns) on a single machine?

I'm wondering what are the drawbacks, from a security point of view, of having more than one service (let's say the web server, the mail server and the DNS server) on the same machine, rather than ...
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2k views

How does lack of SMTP authentication impact users?

My school supplies an email address for its students. To connect to their email server, no authentication is needed for the outgoing mail server. So no user name, or password is needed and no SSL/TLS ...