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.

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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....
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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 …
Dear Experts, we have a mail Exchange domain for example: After that, we configured accepted domain and email address policy, so that another domain could send emails via mail server.

However, when user typed in their web browser:, it redirected to We knew that is expected behavior with the setting but how can we configure so that we have a separated page: instead of

Many thanks in advance!

Env: Window Server 2012R2 Std, MS Exchange 2016

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?


Dear Experts, is there any solution for 2-steps authentication on Exchange on-premise server?

Many thanks!
I have scenario in hybrid environment Exch 2K10 & O365

O365 user trying to send mail to Dynamic distribution group which is in on premises.

Error:- 550 5.7.1 resolver.rst authrequired

Require that all senders are authenticated is checked, I don want to uncheck this for security reasons. Can you please suggest wok around for this one.

We are not creating any objects in cloud, so creating contact with same dynamic group name is ruled out
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
given Facebook friends or running a Facebook group

Are email addresses exportable
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?
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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.

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.
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
Dear All,

I have a question. When my clients send their transactional emails using my provided SMTPS, I process the MTA logs to generate bounces and track emails. I need some guidance here, how would I put my web application in the middle of MTA and the client so if any client sends any transactional email using the provided smtp, it pushes the email to my application first and then my application pushes it to the mta after filtering it.

Thank You
I changed the password on a account and now it is failing.  It keeps asking me to put in the log in and password and when it tests an email, it fails to connect to server.  I have tried deleting the email and reinstalling it.  It won't reinstall it.  I have tried using the old password.  Nothing is working.
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I have Dropcam (now Nest) forward mail to three different email addresses.  Often, one relay entity is very slow (just now, 111 minutes).  This is usually ""  Why and what should I do about it?
I want my mail address back
User get the error message attached

The laptop has been formatted but the issue still exists. It happens only to this user
I have postfix installed on a fedora linux server.  It works for the most part.  I can receive mail and reply via webmail.   It does not work for mail clients.  It will receive mail okay but you cannot sent outgoing via my mail server.  
Plus gmail will not accept my emails because I do not have encryption set up.    Post fix was installed by another admin and I do not want to lose the functionality I have but I need to get up to speed with encryption and being able to send emails from an email client.  
Help please.
I have a custom developed (Mail Service Process) that gathers notification information from various customers, and then builds a notification email and then sends that email through a smtp server (mail chimp).

Some times my (MPS) server or process fails and the emails stop being sent out.  I need to know when we stop sending out emails.  Unfortunately, the server is still running, and the Service is still running, it's just not sending the emails.

I'm thinking I could send (on a schedule, like every 5 or 15 minutes) a genetic "status" email to somewhere external that is watching, and will notify me that the status emails are not showing up, rather than me finding out when a customer realizes they are not getting emails.

Sort of like a deadman switch for outgoing email.

Does anyone know of such a service?  I have seen services that do full send/recv email account verification, but that is not the same.
I have a task to urgently install POP3 service for and existing exim installation on Debian 8.
Which POP3 server is the best? Please link configuration guide if possible.

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.