Adjust the settings on the Security Options tab to prevent this from happening. Since public WiFi networks often do not support traffic on unencrypted protocols. Person sends multiple messages to customers and exceeds the limits set for the SMTP server. This may happen, for example, when a sales Sometimes a legitimate message is rejected. if supported by remote SMTP server option. On the SMTP Delivery tab, select the Use SSL Secure Sockets Layer - A protocol that ensures integral and secure communication between networks./ TLS Transport Layer Security - A follower of the SSL protocol and ensures secure communication between networks.To block messages with large attachments that can overload your server, enable Limit maximum incoming SMTP message size to. number of failed commands in a SMTP session option protects against these applications by closing the SMTP connection automatically after Spammers often send messages using applications that connect to SMTP servers and ignore itsĮrror reports.To block spam messages sent to a large number of recipients, enable Max. If the Exchange server to which you're connecting is running a version of Exchange Server older than 2007, IMAP and SMTP must be enabled by the.To block incorrectly configured DNS entries, enable Block messages if client's IP address has no reverse DNS entry (PTR).To block senders with fictional email addresses, enable Block if sender's domain was not found in DNS Domain Name System - Enables the translation of hostnames to IP addresses and provides other domain related information.Enable the Do not apply these limits to IP address group option and select a group of trusted IP addresses that are not affected by.The dictionary to generate possible usernames. If the SMTP server requires authentication, type username and. Harvest attacks, in which an application connects to your server and uses Kerio Control selects the best method available with this option enabled. number of unknown recipients protects Kerio Connect from Select the Relay Control tab and if not set, check the ' Allow relay only for: ' radial and under this selection, check the box for ' Users authenticated through SMTP for outgoing mail '. Select Configuration > SMTP to open the main configuration screen. number of concurrent SMTP connections gives protection fromĭenial of Service ( DoS Denial of Service - An attack that can overload the server and makes it unavailable to users.), attacks Login to the Kerio Administration interface. Sent from the same IP address after reaching the set limit. number of messages per hour discards any new message you can set the following IP address based limits: For a single IP address An identifier assigned to devices connected to a TCP/IP network.In the administration interface, go to the Configuration > SMTP Server > the Security Options tab section.In Kerio Connect, you can configure several limits for IP addresses to secure your SMTP server: You need to check the following settings in Kerio Connect:Īllow relay only and Users authenticated through SMTP for outgoing mailĮrror: Cannot connect to the SMTP server.Įrror 4.5.For detailed information about configuring the SMTP server, read Configuring the SMTP server. It is recommended to check the SMTP Auth and Relay settings both on Kerio Connect's side and the third-party mail server's side. Improper/Broken Postfix configuration, such as relaying and recipient settings Sending an email to an external mail server without proper authentication There are two main reasons for this error: This error usually happens when users send/forward emails to or receive emails from Postfix mail servers. You will see Error 454 in the email logs and bounce messages sent to users. Sample output: QUIT sent, got reply: 221 2.0.0 Bye Root Causes and Resolution The output of the debug logs shows a Connection Lost error response: Connection lost with : Connection lost. The following are scenarios involving SMTP-related issues, including their root causes and their fixes: eml file for additional information that can be used for further investigation. ( Optional) If possible, gather the source. Choose the Plain Text and Full File options: Gather the debug logs by right-clicking on the log area and selecting the Save Log option. Log in to Kerio Connect Web Administration Console and go to Logs > Debug.Ĭlear the log by right-clicking on the logs area and selecting the Clear Log option from the context menu:Įnable the SMTP logs by right-clicking on any part of the log area and selecting the Messages option from the context menu:Įnsure that the following checkboxes are selected and click the OK button: While reproducing the issue, gather the SMTP Debug logs: This article provides information about the root causes and resolution for known SMTP queries when troubleshooting and reviewing log files. Occasionally, you may encounter issues where email delivery is unsuccessful due to SMTP errors.
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