Articles

IMAP, POP3 configurations, SMTP server-client communication

• Users Cannot Send or Receive Emails

  Overview When a resource is tied up and cannot be used by another part of the mailserver process, the following error is shown in the Mail logs: Result: delayed, Status: 4.3.0 Recipient's mailbox busy...

• Sending Kerio Connect Emails Through SMTP Outbound Relay

  Overview When there is a need to configure SMTP outbound relay (Mail Gateway), the specific Kerio Connect settings in SMTP Delivery should be applied. One specific use case where this knowledge is app...

• Error: "4.5.3 Too many recipients, maximum recipient count exceeded" When Sending Emails

  Overview You may receive similar non-delivery emails (NDR) with the following message: 4.5.3 Too many recipients, maximum recipient count <number> exceeded. This article explains why this error occurs...

• Unable Send Email due to errors 'Cannot connect to SMTP server' or ‘4.4.1 Cannot Connect to Host’

  Overview You cannot send emails to a particular recipient, domain, or mail server. Within the Message Queue in Kerio Connect Webadmin, you see emails with the status “4.4.1 Cannot connect to host.” Th...

• Securing the Kerio Connect SMTP Server

  Overview The Kerio Connect SMTP server has built-in settings to secure the email messages' connection. Misconfigured SMTP may produce the following error in Security logs: SMTP connection from x.x.x.x...

• Temporary local problem while sending or receiving emails

  Overview Users are getting a Non-Delivery Receipt (NDR) email with the following error messages: <xxxx@testmail.com> (<server name> 451 Temporary local problem - please try later) 4.1.1 451 Temporaril...

• Configuring POP3 for Remote Emails and Applying Sorting Rules in Kerio Connect

  Overview When POP3 is connected, the Kerio Connect downloads incoming emails from the remote mail server or domain and stores them into individual mailboxes. Kerio Connect can retrieve messages from r...

• SMTP message size limit causing email issues

  Overview When sending messages to Microsoft SMTP servers, the email is not going through with the following Non-delivery receipt (NDR): The following organization rejected your message: <Server> Diagn...

• Internal Server IP in mail headers

  Overview Mail source headers are providing extended information about the Kerio Connect mail server. If the SMTP server option called Hide local IP in Received headers is checked, the Kerio Connect ca...

• Block messages if client's IP address has no reverse DNS entry (PTR)

  Overview When the SMTP server Block messages, if client's IP address has no reverse DNS entry (PTR) option is enabled, the Kerio Connect verifies the rDNS record during the SMTP session communication....