[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More


Email Servers





Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.

Share tech news, updates, or what's on your mind.

Sign up to Post


starter unlimited plan

Is the email safe?

If I upgrade to
Business unlimited
Premium unlimited
is email more secure

can someone visit a webpage and see my email
using a browser or telnet or command prompt window
C++ 11 Fundamentals
LVL 12
C++ 11 Fundamentals

This course will introduce you to C++ 11 and teach you about syntax fundamentals.

unable to login to ecp and owa on exchange 2013, any help with this would be great.
Hi I am using comcast server for email on Asp.net, I am facing issue while sending email, What is happening is when I am setting from-address of different email domain then its failing and throwing error :

Transaction failed. The server response was: 5.2.0 STOREDRV.Submission.Exception:SendAsDeniedException.MapiExceptionSendAsDenied; Failed to process message
due to a permanent exception with message Cannot submit message. 16.55847:301D0000, 17.43559:0000000094000000000000000200000000000000,
20.52176:140FCC841400101038020000, 20.50032:140FCC848417101044020000, 0.35180:02011330, 255.23226:5A020000, 255.27962:0A000000, 255.27962:0E000000,
255.31418:0201E165, 16.55847:9C000000, 17.43559:0000000068010000000000000100000000000000, 20.52176:140FCC84140010100B002900,
20.50032:140FCC848417101003003600, 0.35180:C9000000, 255.23226:0A004100, 255.27962:0A000000, 255.27962:32000000, 255.17082:DC040000, 0.27745:0A006400,
4.21921:DC040000, 255.27962:FA000000, 255.1494:E9000000, 0.37692:01000100, 0.37948:01000100, 5.33852:00000000534D545000000100, 4.56248:DC040000,
7.40748:010000000000010B01000100, 7.57132:000000000000000000000000, 1.63016:32000000, 4.39640:DC040000, 8.45434:BADA3CA85AC1194EB5D80A8D8905B0EB45004338, 5.10786:0000000031352E32302E313232382E3032303A435934...

If I setup Comcast Username as From-User then it works fine, How i can fix that? Please help
Dear Support

our environment is 2 HUB's & 2 MB  with 2 AD , on VM environment , before for 2 days was every thing works fine until we face an issues with emails sending and reviving and by sending the email and not receive from the other side and from OWA we face also an error ( see the attached ) , after that i mount all the data base on one server only and after that every things works fine !!! now all the database is mounted on one server ,

so i know that there some thing wrong on the other mailbox server , i create a new database and create a test user and let this database mounted on the fault server and try to send and receives emails but still the same issues ? i checked the service the DAG cluster every things works normal .

could you help on this please .
A quick guide on adding multiple SMTP proxy addresses to Users for Office 365
Dear Experts

We have been provided to configure email account in CRM system to send email through the SMTP server using  office365 connector ( SMTP Relay ) the provided account is of without the password (hence in CRM system configured without SMTP authentication) , we were able to configure this account in CRM system and able to send mails but the messages are not getting stored in sent items. to achieve this should we have to go for Authenticate CRM application directly with an Office 365 mailbox, and send mail using SMTP client submission please suggest, thanks in advance.
I am setting up a new HREL 7 server and trying to configure Postfix to send from one of the virtual IPs assigned to the server. I can successfully send mail, but the problem is that when mail is received, the header shows the server's primary IP instead of the virtual IP. It is flagged as spam due to a possibly forged header. The header includes:
Received: from mail.mydomain.com.com (unknown []

What am I missing?

Assumptions (not actual names/IPs):
Server's primary IP:
Server virtual IP = (mail.mydomain.com.com)

DNS records:
mail.abc.com  A
mail.abc.com  TXT   v=spf1 ip4: ~all

/etc/hosts: mail.abc.com

Postfix Configuration: (/etc/postfix/main.cf)
myhostname = mail.mydomain.com.com
mydomain = mydomain.com.com
mynetworks =
inet_protocols = ipv4
inet_interfaces = $myhostname, localhost
I want to build more traffic ,find new customers for my business . So i am confused about EDDM service that it's worth it?

Refer to above link: it's said Barracuda has a list of bad IP : how can we download it?
I would also like to download for SpamHaus & CBL & any other if possible?
I am running MS Exchange 2013 CAS/MDB and an Edge Server in my environment. When I set up the Edge Server I had to run a power-shell command to promote it and join it to the Exchange Server. I am now thinking of going with a different solution for my spam filter such as Proxmox Email Server or Mailcleaner. My question is, do I need to do anything specific to demote the Edge Server? Or can I just install the new appliance and point my firewall to the new mail gateway?

Thanks in Advance.
Protecting & Securing Your Critical Data
Protecting & Securing Your Critical Data

Considering 93 percent of companies file for bankruptcy within 12 months of a disaster that blocked access to their data for 10 days or more, planning for the worst is just smart business. Learn how Acronis Backup integrates security at every stage

I have a two server DAG and need to delete and recreate the databases due to suspected corruption. I am running Exchange 2016 and have 5 active databases. What would be the best way to systematically delete and recreate each database

I have a large outlook.pst file (8GB), that I imported into a IMAP account on our email server (hMailserver running on Windows Server). It looks like during the import some folders failed to import and now are missing on the email server.

Could you please advise is there any tool that I can use to compare the pst archive with the content of the IMAP account (probably the ost file in Outlook) ?
I have critical situation , suddenly any user cant receive mails in my organization , i have exchange 2007 i can send mails but nithing reicved even internal
what i can do
i review all settings which was used before and it is up and running
Dear Experts

We are using offfice 365 SMTP relay to send mails to the external users through the CRM application, i,e option 3 on the following URL
https://support.office.com/en-us/article/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-office-365-69f58e99-c550-4274-ad18-c805d654b4c4 , this CRM system is allowed only to talk with <domain>.mail.protection.outlook.com on port 25 and 587 and rest of the access to the internet is blocked, not access for this CRM system to http/https to the external network.
1. we observed the CRM system workflow triggers the emails to the external network users only when the port 80 is opened for the CRM system at the gateway/firewall level,  we noticed the CRM system gets connected to internet and connects to crl.globalsign.com  and from here it is connecting to office365 smtp and emails are delivered.
2. when we disable access to external network i,e port 80 http blocked for CRM system at gateway/firewall then emails does not flow no packets flow found hence no mails are sent.
3. When only allowed CRM system can talk to crl.globalsign.com  then emails are getting triggered.
can you please help me understand how this office365 is working when it is configured to the CRM system. is it essential that CRM system to be allowed to talk to crl.globalsign.com . please suggest.

We have a small SAAS application, and we want to start emailing our users a weekly email.

Can anyone recommend an approach for this? Does Mailchimp or other similar services allow you to use their API to pull the $Email, $FirstName and $EmailPreferences from your database and then send all of the emails?

Any advice would be greatly appreciated, thanks in advance.
My customer had been getting a few phishing emails, which I could explain as opportunistic. He's the accountant in the school and the sender was supposedly the school director looking for money to be transferred to an account. The reply-to address was somewhere in Poland.  The school's web site has contact details for the school director and accountant so not too hard to  see how a phishing email could be constructed.

It took a bit of a turn when he got a second phishing mail with similar request to transfer money from the same source to a bank account in Spain.  This time though the phishing email was a reply to a legitimate email the accountant had sent to someone with a  sensitive attachment in it. Needless to say, he's concerned how his emails have been compromised and I'm struggling to come up with an explanation.

Their email server is an Exchange 2016 box, fully patched. They have a Sonciwall on the perimeter with OWA allowed access and IMAP and POP3 denied.

Anyone have any idea or explanation how the phisher has access to his emails and attachments??

Is there a way of blocking a delivery receipt from being sent to the sender of an email.  There is when there is a read receipt but how about a delivery receipt
hi guys

We've had an email that looks like it has come from a bank claiming that one of their customers have had a fraudulent transaction on their card from one of our stores. I'm almost certain it is a phishing email of some sort.

I wanted to verify with you guys whether it is likely that the email address has been spoofed.

I won't be able paste the email address it is coming from. But as it claims to be from a bank, the sending server was the following:

Connection  Accepted
Sending Server (mail-eopbgr100089.outbound.protection.outlook.com)
Sending Server HELO
Connection Started
28 Sep 2018 5:45:45 PM GMT+01
Connection Finished
28 Sep 2018 5:45:45 PM GMT+01

Am I right to assume that any 'Bank' that is using Outlook as its sending server is using spoofing tactics?

Dear Experts, we have several Exchange 2016 servers (VMs) in Vsphere 6.5 environment, but one SAN storage is running out of space.

How can I check whether if we can delete some space in Exchange Database? Due to company policy, we have to keep disabled mailuser for a year; but in urgent they can be deleted.

But I'm not sure to check the space which was taken by those disabled accounts. Can  you please help? many thanks!
Determine the Perfect Price for Your IT Services
Determine the Perfect Price for Your IT Services

Do you wonder if your IT business is truly profitable or if you should raise your prices? Learn how to calculate your overhead burden with our free interactive tool and use it to determine the right price for your IT services. Download your free eBook now!

If we don't subscribe to among the lowest-end  O356 Exchange Online,
how can we further secure our email defenses (if we don't purchase
filtering tools like IronPort & Proofpoint)?

I've heard in Postfix forum that they link Postfix server to SpamHaus,
CBL (pls suggest more free Site Reputation services for emails):    can
 Exchange Online implement this?  Can we integrate with Virustotal?

Based on threat intels we get, can we add the hashes into our NIDS
CHeckpoint (assuming email payloads pass through it or in practice
people don't do this?) or Exchange Online??

Will hardening our Outlook client, MS Office, Pdf reader (& all the
'Mobile Codes' softwares) help?
I am about to build a separate, stand alone CentOS 7 server to just run postfix.  I work for a fairly large company that has 3 email domains, for ease lets call them 1.com, 2.com and 3.com.

1.com and 2.com will be having that email redirected to mimecast (www.mimecast.com), however 3.com needs to have the email sent to a different location (an internal Exchange server).  The reason for this is that 3.com will, in a few months be moving to Office365.

My question is, whats the best way in postfix to say "if 1.com or 2.com send ->  relay it via mimecast, and for 3.com send it another destination.

I have worked with postfix quite a bit, however mainly using basic configs, or basic mail relay for one single domain.

Thanks for your time,
I need some help with this, I have 3 users that when multiple users with different email providers send them emails they get this bounce back. not with all the outside users happens either. other Users inside my organization have no problem receiving from this users. i have checked their blocked senders list, spam folder and filter. I run this command from the power shell (Get-MailboxJunkEmailConfiguration  username).blockedsendersanddomains and i see just one adress in one user not related with the bounce backs, the other two users have no emails blocked.

The response was:

550 permanent failure for one or more recipients (user@domain.com:blocked)

Final-Recipient: rfc822; user@domain.com .com
Action: failed
Status: 5.0.0
Remote-MTA: dns; d91072a.ess.barracudanetworks.com. (an IP the company does not have., the server
 for the domain domain.com)
Diagnostic-Code: smtp; 550 permanent failure for one or more recipients user@domain.com:blocked)
Last-Attempt-Date: Mon, 01 Oct 2018 10:27:32 -0700 (PDT)

any help would be appreciated as i have no more ideas on this.
Currently using O365 and wanted to know if there are any commands that could list all mailboxes that utilizes a Safe Senders List as well as to list the contents of their Safe Senders List.
We have several office that utilize gsuite, but others prefer O365. The issues that gsuite doesn't work well with outlook. Can we  coexisting platform with gsuite and exchange server setup. So essentially others can continue to use gsuite while others that prefer outlook can use it.
we upgraded zimbra 8.6 to 8.8.9 version. now zimbra shared calendar cannot get work with outlook. it asking for user name & password. even if entered correct user pwd, it not success.
we can see below error from non authenticated browsers.

in log files we can see : cat  nginx.access.log
HTTP/1.1" 401 520

please help

Email Servers





Within Internet message handling services (MHS), a message transfer agent or mail transfer agent (MTA) or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture. A MTA implements both the client (sending) and server (receiving) portions of the Simple Mail Transfer Protocol (SMTP). The terms mail server, mail exchanger, and MX host may also refer to a computer performing the MTA function. The Domain Name System (DNS) associates a mail server to a domain with mail exchanger (MX) resource records containing the domain name of a host providing MTA services.