Email Protocols





Interactions between email servers and clients are governed by email protocols. The three most common email protocols are POP, IMAP and MAPI. Most email software operates under one of these (and many products support more than one).  The correct protocol must be selected, and correctly configured, if you want your email account to work.

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

Sign up to Post

My OS is win 10 Prof 64 bit and I use office 365 and Outlook owa for my msn email account.  How do I get educated that the sender of an email is really the sender and not someone else emulating him or her.   As I get so many emails I would like to be educated on this, is there any site or video where I can discern more knowledge.  Thank u and regards.
Cloud Class® Course: CompTIA Healthcare IT Tech
LVL 12
Cloud Class® Course: CompTIA Healthcare IT Tech

This course will help prep you to earn the CompTIA Healthcare IT Technician certification showing that you have the knowledge and skills needed to succeed in installing, managing, and troubleshooting IT systems in medical and clinical settings.

How to restore my SENT emails in
They disappeared.  I did NOT delete them!!!!! Thousands of them.
I am using the web interface.  I have not downloaded them to my local drive.
I downloaded the email recovery add in but am NOT getting any SENT emails. Just some of my inbox.  is the link I am using even though my email address says "HOTMAIL".
I don't want to recovery any of my INBOX.  Just my sent.  I have thousands  of SENT messages that I need to recover.
What is the correct process to use to set up an Outlook 2016 Gmail account to save emails to a PST file instead of an OST file?
We have a single user who is unable to send email outside of our organization due to multiple kickbacks with following NDR
Remote Server returned '550 5.7.501 Service unavailable. Banned Sender
I have verified by searching the various online spam lists ( spamhaus, etc) that our domain is not on any list and the issue does not seem to be effecting any of our other users. This user had his account hacked last week and we discovered it was used to send a large amount of spam before we reset his account.
I am unable to find a solution to resolve kickbacks for a single email address.
There's an external application server (IP a.b.c.d)  that send email blasts to a
team/dept in our organization but we block this IP in our exchange/domain
because it is sending with the sender in the email header as

What are the risks & mitigations we can put in place if we were to permit a.b.c.d
to bypass from Norelay (sender and recipient email address from same domain)
Outlook 2010 user has e-mail hosted by Gmail (IMAP), and has created around 50-60 subfolders.  Auto archive will not work on those folders, which requires him to do a manual cleanup archive of the Gmail account and all subfolders.  This works fine, but has to be done manually every so often.  Is there a better way and without 3rd party software?
I'm trying to understand how to track messages around Exchange to thwart phishing attempts quickly.

Is there a way to see if a message was opened?

Is there a way to see if an attachment was opened?

Is there a way to see if a user forwarded a message?

Thank you,
We have been struggling with setting up our website on a GoDaddy Virtual Private Server. Please Help!

We have a .net program that connects to First Data to process credit cards. It running on a Windows 2012R2 + Plesk Virtual Private Server hosted at GoDaddy.We need to send confirmation emails from the server after a transaction is processed. I am attempting to send an SMTP email on a GoDaddy Plesk VPS and am having difficulty with the syntax.  Here are examples of what has been tried with the corresponding error messages.

I am having a customer that is attempting to email us and is getting an error on their email servers.

Connection for delivery was deferred by "my.mail.server"
 and they are getting a 4.4.2 error that is coming from my mail server

Mail server is running postfix, but I do not see this particular email address in the logs. I see other email addresses from the same company successfully show up in the logs, but not this particular one.  Client is putting additional pressure to figure out root cause.

Any thoughts?

Dear Experts, we are having 1 Exchange Mail server and 1 AD server with domain:, with about 1000 users and 10 TB of mail data

Now we'd like to change the domain to:, and remain the same users' data

Is it possible? If so, how can we do it?

Many thanks!
Free Tool: SSL Checker
LVL 12
Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

email that I'm sending is now going to my customers spam boxes.  kinda happened out of the blue.  its not bulk emails.  its individual emails the i type with info for my clients.  i do copy/paste some info that goes into each email as well.

been working fine for years...its just all of the sudden everyone is saying that email is going to their junk boxes.  

its my own private domain email, i use gmail as the client for checking and sending it.

i havent changed anything on my end.  what do I need to look for to see what is going on?  TIA
as many others I have also problem #550 4.4.7 QUEUE.Expired; message expired ##
Exchange 2010 works fine for years, suddenly is refuse to send mails to some e-mail addresses.

I checked, MXtoolbox
reversed dns (PTR) is set
in exchange send connector FQDN is filled in and is the same as the PTR

please advice,

Many thanks Victor
I have a Exchange 2016 setup along with a Forcepoint Spam filter, i have configured my send connector to relay to force point, along with a receive connector to receive those IP addresses from Force Points servers. I can telnet to my exchange server, i can send internally, i can send externally, but i cannot receive externally, as i get a NDR saying i am stuck in a loop, or i get no NDR and its lost forever....anyone can help that would be awesome....

I have a strange Problem. I am not getting some emails from some recipient, the TXT emails are delivered without any problem but with PDF attached emails are not passing through.
Even Message tracking it not showing but in SMTP receive logs its showing delivered

8847,>,250 XProxyFrom accepted,
8847,<,MAIL FROM:<> SIZE=0 AUTH=<>,
8847,*,SMTPSubmit SMTPSubmitForMLS SMTPAcceptAnyRecipient SMTPAcceptAuthenticationFlag SMTPAcceptAnySender SMTPAcceptAuthoritativeDomainSender BypassMessageSizeLimit SMTPSendEXCH50 SMTPAcceptEXCH50 AcceptRoutingHeaders AcceptForestHeaders AcceptOrganizationHeaders SendRoutingHeaders SendForestHeaders SendOrganizationHeaders SendAs SMTPSendXShadow SMTPAcceptXShadow SMTPAcceptXProxyFrom SMTPAcceptXSessionParams SMTPAcceptXMessageContextADRecipientCache SMTPAcceptXMessageContextExtendedProperties SMTPAcceptXMessageContextFastIndex SMTPAcceptXAttr SMTPAcceptXSysProbe,Set Session Permissions
2018-03-04T13:01:48.037Z,GSEXCHMC1\Default GSEXCHMC1,08D57BA60716263A,263,[2002:c864:6406::c864:6406]:2525,[2002:c864:6406::c864:6406]:8847,*,08D57BA60716263A;2018-03-04T12:54:14.609Z;12,receiving message
<,RCPT …

So we are working to configure Mandatory TLS security between 2 email domains. We have control of one, which we need to get this configured for.

They are currently using Office365 which routes through Mimecast for email filtering etc.

So my understanding of it is that we configure this on Mimecast only for incoming and outgoing mailflow, however, I am struggling to see how it works correctly, when it needs an SSL certificate from Office365 in order to work correctly?

Do we also need to configure inbound and outbound connectors for this TLS requirement on Office365?


I am  writing send-mail program in android. it is working OK.
but in case, if we have problem in connecting smtp server or it might bounce back for some other reason..
(My question here  is )
if the sent mail is bounced back for some reason, how to judge inside the android code for the smtp errors and retry sending it later...
several times or for specified tries till it reaches the receiver..
Can any  one  share the code for  queuing emails.. and handling smttp errors. etc.
Thanks in advance
I have a c# program I am working in that I did not originally create.  I need to add an email element that will create a PDF with graphics (like the attached) authenticate with an email server (like gmail, microsoft or similar) and send that email to a specified address.

I am not sure where to begin, especially on creating the data based graphic.

My ex boyfriend hacked me and deleted/or changed my Gmail  account how can I get it back?
Is there an easy was to set up email (other than standard received notice) to determine if an email sent has been received. We keep having issues with our emails not received.
Cloud Class® Course: Certified Penetration Testing
LVL 12
Cloud Class® Course: Certified Penetration Testing

This CPTE Certified Penetration Testing Engineer course covers everything you need to know about becoming a Certified Penetration Testing Engineer. Career Path: Professional roles include Ethical Hackers, Security Consultants, System Administrators, and Chief Security Officers.

We have a legacy software that does not support TLS so we relay the emails via an IIS relay that authenticates and send out via Office 365.

Emails to certain recipients are bouncing with the NDR 550 5.6.11 SMTPSEND.BareLinefeedsAreIllegal

This has just started recently about 2 months ago .

This Microsoft links explains why -

 What's a bare line feed in email messages?

Usually each line of characters in an email message ends with a carriage return followed by a line feed (CR LF). A bare line feed is a line feed (LF) character that is not immediately preceded by a carriage return (CR) character. In other words, instead of a line ending with CR LF, it ends with only LF.
This worked fine before, why did it stop working recently?

Until recently, Office 365 automatically removed bare line feed characters from mail to help it get delivered to recipients using older email servers that don’t support chunking and the BDAT command. The support for BDAT is required by the email industry standards referenced in RFC 1830. In an effort to better support security standards, like DomainKeys Identified Mail (DKIM), Office 365 no longer removes bare line feeds from messages. As a result, messages sent to users with older mail servers may be more likely to be rejected.

Their suggestion is to make changes on the recipients server which is not possible so what can I do on our end to fix this?
Our client (a sort of golf travel company) in the UK regularly sends out email worldwide to their clients. They are now receiving bounce-backs in German, making it difficult for my client to resolve them. The user sending the orginal emails is

I have contacted  the ISP (Fasthosts in the UK) and they understandably say "This would only happen if the e-mail you are sending to is hosted on a German server as the bounce back is sent from the server rejecting the e-mail." however, our client receives these from all over the world always with the same formatting, so they seem to be coming from the same generating program, if not the same server?

I attach some of the bounce messages (they're in Outlook Item file format).

I suppose the other issue is what are these, or what's causing, the bounce-backs in the first place?

I am sure those of you who "enjoy" trawling through email bounce headers will find this a fun challenge :-)
Help! I spent a few hours drafting a long heartfelt email to my children and when I hit save it save draft. Now I have gone to my saved draft folder and it is not there. Is there anyway to still retrieve it or am I sunk?
I would like to make a parse of postfix mail log in an HTML/PHP page with a search bar and then creating a dynamic table with all these tags. when the table is done I should be able to click on the "Date" and another page should open with others info about that log *(2)

I will copy an example of a log

search: from: ...... to: ...... date: from: .... to: ....

Eg Table example: Date | time | from: Jack | to: John | status:


status detail

809318:Jul 11 14:13:50 amail-2014 postfix/smtpd[17127]: 78F5E83F28:[]
809320:Jul 11 14:13:50 amail-2014 postfix/cleanup[18135]: 78F5E83F28: message-id=<>
809324:Jul 11 14:13:50 amail-2014 postfix/qmgr[27711]: 78F5E83F28: from=<NO-REPLY@MOLEX.COM>, size=30390, nrcpt=1 (queue active)
809325:Jul 11 14:13:50 amail-2014 postfix/smtp[11782]: 78F5E83F28: to=<*****@SYLEX.SK>,[]:25, delay=0.73, delays=0.59/0/0.01/0.13, dsn=2.6.0, status=sent (250 2.6.0 <> [InternalId=50607599648815,] Queued mail for delivery)
809326:Jul 11 14:13:50 amail-2014 postfix/qmgr[27711]: 78F5E83F28: removed
809323:Jul 11 14:13:50 amail-2014 KLMS: not processed: …
I got a mail from was it real or not please tell me
I have one client that cannot email me.. They receive a bounced back message saying;

550 Verification Failed
No such user here
Sender verification failed

I can however email them. But they cannot reply.

None of their emails from their domain will come through, however I have been guaranteed from my ISP (crazy domains) that there are no blocks on my end. However i do know of another company who are with crazy domains are experiencing the same problem with the server  

As I run my ow  business, my only option is to change hosting companies in the hope that works.

Would love an easier fix

Email Protocols





Interactions between email servers and clients are governed by email protocols. The three most common email protocols are POP, IMAP and MAPI. Most email software operates under one of these (and many products support more than one).  The correct protocol must be selected, and correctly configured, if you want your email account to work.