Occasional Delivery Rejects with large MX lists
(Doc ID 1516001.1)
Last updated on MAY 18, 2021
Applies to:Oracle Communications Messaging Server - Version 6.2.0 and later
Information in this document applies to any platform.
In this service request the admin was seeing occasional NDRs for email messages that should have been delivered to a valid external system.
By enabling master_debug on the channel that generating the NDR messages we found the mx lookup for the domain was being truncated and that was causing the delivery failures.
This is what the tcp_outbound channel's master_debug log looks like when the message is processed correctly in the. Below you can see the last record is truncated, the customer actually has 27 records for this one MX, MTA's buffer for the MX results isn't large enough to hold all 27 records so it processes 14 and truncates anything past the buffer.
The MX record exceeds the DNS response packet size limits of the MTA, which is 512 octets. The result is truncated, so we only get the first 14 entries.
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