DOCUMENT:Q271545 13-DEC-2000 [exchange] TITLE :XCON: Message Timeouts and Open Retry Timeouts PRODUCT :Microsoft Exchange PROD/VER::5.5 OPER/SYS: KEYWORDS:exc55 ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Exchange Server, version 5.5 ------------------------------------------------------------------------------- SUMMARY ======= This KB article discusses the differences between message timeouts, and Open Retry timeouts. MORE INFORMATION ================ As an example of how these two issues may be confusing, look at the following two articles in the Microsoft Knowledge Base: Q157630 XCON: Adjustment of Connection Retry Values on Override Tab Q178539 XCON: How to Adjust Message Timeouts for the Exchange MTA At first glance, these articles can seem contradictory; it is unclear whether mail is returned undeliverable after 24 hours, or after seven days (in the case of Normal priority mail). Message timeouts define how long a message has to live within the message transfer system before the system returns the message undeliverable. A concept that is very similar to the Time to Live (TTL) value in IP packets. Open Retry intervals, on the other hand, define the length of time during which the message transfer agent (MTA) tries to connect to another MTA to deliver a message before giving up, and then returning the message as undeliverable. Consider these two different hypothetical scenarios, assuming the simplest configuration of only two servers (MTA1 and MTA2): Scenario 1: MTA1 attempts to send a message to MTA2, but MTA2 is down. Because MTA1 cannot open a connection to MTA2, MTA1 falls into a state of Open Retry, and the Max Open Retry counter starts to increment. By default, the retry interval (the length of time between connection attempts) is 600 seconds, or five minutes. By default, MTA1 tries to make a connection to MTA2 144 times before it giving up, and then returning any messages, which were queued for MTA2, to their originators as undeliverable. 144 retries multiplied by 600 seconds is equal to 86,400 seconds, which is approximately 24 hours. Thus, if MTA1 has mail to send to MTA2, and MTA2 is down for 24 hours, all mail, regardless of the priority, that was bound for MTA2 is returned as undeliverable. For additional information, click the article number below to view the article in the Microsoft Knowledge Base: Q157630 XCON: Adjustment of Connection Retry Values on Override Tab Scenario 2: MTA1 has mail queued for MTA2, but before it completes the delivery of all the mail, MTA1 shuts down; after a while, MTA1 is back online. The mail that is in the MTA1 queue does not timeout until the MTA on MTA1 detects that the default timeout period for the priority of a given message has elapsed. The defaults are two days for High priority, seven days for Normal priority, and ten days for Low priority messages. Thus, if MTA1 has mail queued for MTA2, and MTA1 shuts down completely for five days, when MTA1 is back online, all of the High priority mail that MTA1 had queued for all destinations is returned as undeliverable to the message originators. However, messages with a Low or Normal priority remain in the queue until they are delivered. For additional information, click the article number below to view the article in the Microsoft Knowledge Base: Q178539 XCON: How to Adjust Message Timeouts for the Exchange MTA The importance of this issue is determined by which server is down: the server that has the mail queued (the Source), or the server that should receive the mail (the Destination). If you have more than two MTAs in the site, or more than one route, which a message can use for delivery, then message rerouting factors into the equation. Remember that the MTA can reroute mail that is queued to non-secured queues, such as the X.400 Connector, Site Connector, Dynamic RAS Connector, and other MTAs. The MTA cannot reroute mail that has been queued to secured queues, such as the Internet Mail Service, and the Microsoft Exchange Connectors for MS Mail, cc:Mail, Lotus Notes, GroupWise, SNADS, and PROFS. Additional query words: ====================================================================== Keywords : exc55 Component : MTA Technology : kbExchangeSearch kbExchange550 kbZNotKeyword2 Version : :5.5 Issue type : kbinfo ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. 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