Category Archives: POP3/IMAP

IMAP connection error – UID corruption detected

Recently in one of the IMAP application were getting complaints on accessing the emails via IMAP.

So enabled the imap logging to see the results

Set-IMAPSettings -Server “MBXservname” -ProtocolLogEnabled $true

After going through the lots we were getting the below error message UidCorruptionDetected


Reason for this error:
Don’t access a mailbox with outlook web access while Outlook has an open connection to that mailbox using the IMAP client protocol .
If you do leave Outlook with IMAP access to a mailbox and access that mailbox from an alternate client, you might have some UID errors to accept when you get back to Outlook.
Example when an application requires either POP/IMAP connection to retrive the emails from Exchange better to choose any one of the connection type and not to access from multiple locations with different protocols.

Also another reason is if the IMAP account is configured on a application and if the application is configured to receive thousands of emails  daily, each and every time when the connection is established the  client app will try to access the entire set of emails. This will make this user account to exceed all the IMAP connection types and will make this mailbox logical UID corruption. So if we have any application accessing using IMAP connection then we need to make sure that an automation job from the application is configured on the client  side to purge the older emails which will solve the problem.

Solution :

Since its mailbox corruption , repairing the IMAPID corruption type will solve this problem.

New-MailboxRepairRequest -Mailbox “mailboxname” -CorruptionType ImapID

Thanks & Regards
Sathish Veerapandian

POP3 Error Msg=UserConnectionLimitReached

Recently in one of the Exchange 2013 environment POP3 clients started getting the problems in downloading the emails from the server.

The strange issue was users were unable to download the emails intermittently and it was not permanent for POP3 accounts.
When this issue occurs the POP3 accounts will stall for a while and later after some time it would start collecting the emails from the server without any issues.

This really looked strange and inorder to troubleshoot further enabled the POP3  protocol logging by the below command

Set-POPSettings -Server “CAS01” -ProtocolLogEnabled $true

After a while looked into the POP3 logging and strange to see the below message


This issue is happening, because the POP3 connections are sending more requests to the server.

This  is the main reason for the application to intermittently drop the connection.

When the connection limit  per user exceeds the default allowed limit, the connection will be forcibly closed by the mail server. And then this connection reset will happen after 4 minutes after which the client can reestablish the connection , download the emails until it reaches the threshold limit of per user.

The default value for the single user is 16

Can be seen from EAC – Servers – Edit – POP3 

Also can be seen by  running Get-POPSettings | fl


So the POP3 Throttling policy allow the counter reset after 24000 milliseconds . So when the user connection limit exceeds the default value he wouldn’t be able to connect till the next counter reset happens.


So the POP Connection limit can be increased by running the below command

Set-POPSettings -MaxConnectionsPerUser  “connectionvalue”

Its important to note that both the POP services POP& backend needs to be restarted after this change to take effect,so we can go ahead and run the below command for the restart of the services.

Get-Service *POP* | Restart-Service

Additional Info:

The POP3 throttling policy value can be seen by running the below command:

Get-ThrottlingPolicy -Identity Default* | fl POP*

POPMaxConCurrency – The PopMaxConcurrency parameter specifies how many concurrent connections a POP user can have against an Exchange server at one time. A connection is held from the moment a request is received until a response is sent in its entirety to the requestor.
POpMaxBurst-  The PopMaxBurst parameter specifies the amount of time that a user can consume an elevated amount of resources before being throttled.
POPRechargeRate – The PopRechargeRate parameter specifies the rate at which the user budget is charged back
POPCutoffBalance – The PopCutoffBalance parameter specifies the resource consumption limits for a user before that user is completely blocked from performing operations on a specific component.

There were Get-WorkloadPolicy IMAP,POP commandlets present before Exchange 2013 CU6 , but later now these commandlets have been removed post CU6 and replaced with Set-SettingsOverride but strictly this Set-SettingsOverride command should be used only under the supervision of Microsoft Support professional.

These values also can be modified based on the requirement , just in case if we have any applications which requires these values to be modified as per the requirement.

Thanks & Regards
Sathish Veerapandian

Quick Bites – Troubleshooting POP and IMAP connectivity issues in Exchange 2013

In this article lets have a look at troubleshooting POP and IMAP connectivity issues in Exchange 2013.

First lets have a basic requirements  to check what are the features and things that needs to be enabled in-order for these services to work.

What ports should be used by the clients for each configuration : –

Port 25 for SMTP with or without TLS, anonymous authentication; (Outgoing)
Port 587 for SMTP with TLS; (Outgoing)
Port 143 for IMAP  without TLS (Incoming);
Port 993 for IMAP with SSL/TLS (Incoming)
Port 110 for POP3  without TLS (Incoming);
Port 995 for POP3 with SSL/TLS (Incoming);

Ensure that all the required ports are open in your firewall accoding to the configuration you have ( with or without TLS). Probably we can do a telnet from externally and see if we get a proper banner.

For POP – Telnet domainname 110
FOr IMAP – Telnet domainname 143

For TLS to work do we need to install any certificates on the servers : –

You should create certificate including your CAS server FQDN and Mailbox FQDN as the SAN name. It should not be self-signed certificate. You should get it from an internal CA or a public CA. Then assign the services SMTP, POP3, IMAP and IIS to this certificate only then it will work.

Do we need to configure anything on the server for POP and IMAP Authentication : –

For Authentication type for POP and IMAP Services, we can choose to use plaintextlogin or securelogin. You can refer to It defines how the application provide the username and password to do authentication.

Below things can  also be checked for Troubleshooting POP and IMAP issues : –
We Can run Test-PopConnectivity and see the results
We Can run Test-imapconnectivity and see the results
Use the remote connectivity analyser for IMAP and POP and see the results

Run the below commands to see the POP and IMAP settings
Get-POPSettings -Server CASservername
Get-IMAPSettings -Server CASservername

Restart your POP3 service and see the results
Check if your POP3 service have valid certificate assigned
Run Get-ExchangeCertificate and see if the certificates are assigned for POP and IMAP services.

Check your ports config and ensure they are correct
Port 110 for POP3  without TLS;
Port 995 for POP3 with SSL;

If you have configured POP and IMAP with either SSL or TLS then a valid certificate should be configured for the same to respond to SSL or TLS(depends upon what type you choose)

Check the incoming and outgoing mail server in Outlook settings

We can enable the trace log and open the log in the location.

Please refer to to set the location and enable the log.


Sathish Veerapandian

MVP – Exchange Server

Steps to configure POP3 in Exchange 2013


In this article we will be looking into how to configure POP3 in Exchange 2013.

The configuration steps are similar to Exchange 2010 unlike here we have 2 pop services running up Microsoft Exchange POP3 service – Running on CAS server role

Microsoft Exchange POP3 backend service – Running on Mailbox server role

Similarly we do have Microsoft Exchange IMAP service – Running on CAS server role

Microsoft Exchange IMAP backend service – Running on Mailbox server role

Below are the steps to configure POP3

 Open EAC – Click on Servers and choose the appropriate Client access server



Select POP3 in the options below


Now we have options to configure the POP3 settings

Here we got to choose the logon method which should be decided according to our requirement

Also we have the message sort order which will let us to download the copy of emails from server according to the type chosen


Now we need to enable the binding if we have chosen the SSL connection.



We have the session idle time out settings, Connection limits which can be configured.

Also we do have the maximum connection from a single user which will help us to keep any unauthorized access from any device

Issue: Unable to send mails from IMAP/SMTP clients.

Recently i came across an issue with unable to send emails externally to our domain from IMAP/SMTP clients and found an solution for the same

Hope this would be helpful for others if similar issue occurs

Issue: Unable to send mails from IMAP/SMTP clients.
Error: 5.7.1 The client does not have permission to send as this sender.
Resolution: The sender specified in the MAIL FROM field of the SMTP protocol conversation is an address in an authoritative domain.
However, the session doesn’t have the ms-Exch-SMTP-Accept-Authoritative-Domain-Sender permission. This might occur if a message was submitted from the Internet to an Edge Transport server from a sender address for which the Exchange organization is authoritative
 Shell Command#
Get-ReceiveConnector “Default SERVER01” | Add-ADPermission -User “NT AUTHORITY\ANONYMOUS LOGON” -ExtendedRights “ms-Exch-SMTP-Accept-Authoritative-Domain”
Get-ReceiveConnector “Default SERVER01” | Add-ADPermission -User “NT AUTHORITY\AUTHENTICATED USERS” -ExtendedRights “ms-Exch-SMTP-Accept-Authoritative-Domain”

A related article which talks about the permission and error:

Exchange 2007 Transport Permissions Model


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