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 client who often sends (exchange) external  e-mail to couple hundred recepients in single mail
and there is a problem because some recipients sends  error "dsn=4.0.0, stat=Deferred: Connection refused by  remotehost."

I presume that is because of mass mailing?
What is the best practices for sending this kind of mails(couple hundred recepients)?
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When you type in in a web browser, theres all the work of resolving the name into an ip address and then your packets are sent from your computer to the EE web server and vice versa, going through routers around the web, right?

Contrast that with an email?  I was explaining to someone that large attachments in an email might cause the email to not be delivered as it routes its way through the web. Then I wondered... is the email actually going through  mail servers on the web and being reforwarded? Or just routers (on the backbone?). If it's just routers, do they actually care how big the total email is? It's just a lot of packets being sent in the same direction.

ie - is there really a limit to an attachment size limit in email OTHER THAN at the sender or receiver email server?  Yes, the sender server or receiving server can set limits to the size of the attachment.  But after resolving the MX record and sending to the receiving server.... what could get in the way?

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....
There is an application in the environment that sends out a thousand messages each month via SMTP on a scheduled date and time.  I have been asked to verify that every message has arrived and been processed successfully by the Exchange servers (the SMTP server has, in the past, encountered issues forwarding mail).

Is there a log file on the Exchange servers somewhere that contains metadata information that I can query via PowerShell?

I don't want to check every mailbox in the environment to see if it contains a specifically worded message, since that message can be deleted by the recipient upon arrival -- not to mention the time and resource utilization that would be required.  

Any thoughts or suggestions on how to make this happen?
My boss has a new iPhone8. I've set him up to access the IMAP server at the office. Inbox works just fine and he can send messages. The problem is that the Sent and Trash folder on the iPhone do no synchronize with the server. Apparently, this is not an uncommon problem since I've found lots of posts about it. However, none of the instructions I've found so far seem to work. How do I do this?

The mail server is Dovecot IMAP. The iPhone is using the normal mail facility, nothing special or 3rd party. The selected server setup is 'Other'. Inbox synchronization works. Messages deleted on the iPhone, and sent messages are not synchronized with the corresponding folders on the IMAP server.

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?


The user has tens of thousands of past gmail messages.  They appear to be in "All Mail" folder in gmail.    Gmail will delete about 100 at a time.

Is there a way to delete a larger amount?

The  Mail  Application on the Mac keeps trying to synchronize them, which slows down the computer.

Hi Folks,

I have the following code to get the attachments form Email, now I need to write the attachments to a detination on my desktop. How should I apply the outputstream to write the attachment files to the destination?

public class ReadMailAttachmentAndAppendToFile extends AbstractTransformation {

	public void transform(TransformationInput in, TransformationOutput out)
			throws StreamTransformationException {

		String contentType = "";

		try {

			getTrace().addInfo("java map started");

			// Get the all of the attachments
			InputAttachments inputAttachments = in.getInputAttachments();
			OutputAttachments outputAttachments = out.getOutputAttachments();

			Collection<String> ContentIDs = inputAttachments
			Object[] arrayObj = ContentIDs.toArray();
		//	getTrace().addDebugMessage("Array object initialized ");
			int attachmentCount = arrayObj.length;

			// Check if there are attachments.
			if (attachmentCount > 0) {
				// Grab the contentIDs that identify each attachment.

			//	int xlsCount = 0;
						"*** Attachments count: " + attachmentCount);

				for (int a = 0; a < attachmentCount; a++) {
					String contentID = (String) arrayObj[a];

					// Grab the individual attachment by its contentID
					Attachment attachment = inputAttachments

					// Get the contentType which contains the filename.
					contentType = 

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This new CentOS server (Postfix 2.10 and Dovecot 2.2) has a handful of users who are connecting using IMAP. None of them can see any of the folders, neither "Inbox", "Sent", nor any of the other ones. Sending e-mail works fine, arrives at recipient's mailbox, but doesn't show in sender's mail client.
What am I missing?
How can I disable the Gmail email account security alerts?

An organization I am consulting for had their Veeam backup email alerts setup using a single Gmail email account that accesses this Gmail account using the SMTP email protocol.

The Veeam backup program on 40 Windows computers sends alerts to this Gmail email address everytime that the Veeam backup succeeds, fails, or has any issues.

These users often travel with their laptops and I am constantly receiving Gmail security alerts related to this email account.

So is there any way that I can disable the Gmail email account security alerts for this Gmail email account?
Dear Experts, is there any solution for 2-steps authentication on Exchange on-premise server?

Many thanks!
When I go to the website and type in the email domain name of my organization the SPF & DKIM results pass but for the DMARC test I receive a message that says "Thank you for getting started with DMARC. You are currently at the lowest level and receiving reports, which is a great starting point. Please make sure to review the reports, make the appropriate adjustments, and move to either quarantine or reject soon. Additional information about reporting tools can be found here" (see the second screenshot below).

When I click on here I am taken to this website

What values do I need to change or what settings do I need to change within my external DNS server records so that I will pass the DMARC test for this website?

I currently have this TXT record setup within my public DNS records for DMARC:      3600      IN      TXT      "v=DMARC1; p=none;;"

PLEASE NOTE: The actual domain name has been replaced with the word domain above and has been whited out in the screenshot for privacy purposes.

Domain results
i have install postfix on ubuntu 16.04 for send-only mail.
when i send mail nothing happend nor error and  don't send mail.
service status on postfix  is
fatal: bad numerical configuration: mailbox_size_limit = 20M
fatal: bad numerical configuration: mailbox_size_limit = 20M
warning: process /usr/lib/postfix/sbin/local pid 12388 exit status 1
warning: /usr/lib/postfix/sbin/local: bad command startup -- throttling

what is wrong here what should linit be?
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 trying to follow an online tutorial which would allow me to send an email using PHP Mailer. I previously had some problems with my hosting company not supporting php mail() but this has been resolved and I am now able to send an email using a script which uses php mail().  However, I've been advised to use PHP Mailer, so started following a tutorial. As far as I can understand I've followed all the steps in the tutorial and the following should work.  The code is below....

I am testing this on my live server and WAMP developer server and having no success at either.  Any advice or guidance would be really appreciated with this. I have been really struggling over the past couple of weeks to create a page which sends emails.

Many thanks


$msg = "";
	use PHPMailer\PHPMailer\PHPMailer;
	include_once "PHPMailer/PHPMailer.php";
	include_once "PHPMailer/Exception.php";
	include_once "PHPMailer/SMTP.php";

if (isset ($_POST['submit'])) {
	$message = $_POST['message'];

	if (isset($_FILES['attachment']['name']) && $_FILES['attachment']['name'] != "") {
										//$_FILES is a global variable we use when sending attachments
	$file = "attachment/" . basename($_FILES['attachment']['name']); // - The basename() function returns the filename from a path.
										//we are uploading to "attachment" folder


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Our Proofpoint support expired so I can't open a ticket with them.  We are using Proofpoint Protection Server

I am trying to obtain the outbound mail stats in Proofpoint  using the reports feature for Category = Firewall, Data Options Reports for Route = Outbound and keep getting 0 for results no matter what combination in the reports I use. I have also tried using the instructions here 
and do not obtain any results.

The admin told me there is not a canned report for this, but I'm wondering if we don't have something set up in the configuration to parse the logs to see outbound traffic.

Any thoughts on either how to fix it so I can obtain results from the reporting or UI Stats, or another way for me to obtain the outbound mail stats?

Thank you for you help.
can someone tell me what the smtp setting Use domain name system [DNS] "MX"records to route mail automaically does?

im just curious how it works.

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i have exchange server 2010 with pop3 connector. when i send an mail it's appear that is coming from my pop account.
can i do it on office365 ? or any other hosted company ?
If I am sending out a bulk email that includes a picture for a header, does it matter if the link to the picture is http or https?

I seem to remember from days past that https image links could cause some problems. But I'm not sure if that was from the dark ages and is no longer relevant. Or is that still important?

I have a global address list. When i click on address book go to tools-->options--> when sending email check email addresses in the following order.
The options are
1) start with global address list
2) start with contact folders
3) custom

when opening the address book, show the following list first - choose automatically is selected

The problem is that "start with global address list" doesn't work. I have to make it work. is there anything i can do via power shell that can solve this. Currently the users have custom and global address list is the first with suggested contacts in second and the rest follow. this works. We using exchange 2010 with outlook 2010. What can i do at server level to fix this issue. We dont want to goto individual users. approx 2000 users
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 user with no unity mailbox but gets the mailbox quota message "Your voice mailbox has exceeded the quota warning threshold specified by your administrator." How do I export all SMTP Proxy Addresses and verify that the user affected doesn't have their email address attached to another mailbox. Unity version is
I have a client who's having me move his website to a new host. His email accounts are on G Suite and have his domain after the @, but were originally created through Wix when he had a Wix website. I'm able to access his email via an IMAP configuration on my email client (which happens to be Thunderbird) using gmail's mail server,

It appears to me that his email has nothing to do with Wix. However, he still has a Wix account that lists his email addresses as associated with the account.

I'm now about to change his domain's name servers at his registrar (which is not Wix) to point the domain to the new host. Does it sound like I'm correct in assuming that his email, which has his domain after the @ sign, will be completely unaffected by this?


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.