Periodic Delay before MTA Responds to RCPT TO
Last updated on JANUARY 12, 2018
Applies to:Oracle Communications Messaging Server - Version 5.2.0 and later
Information in this document applies to any platform.
SMTP clients and remote MTAs occasionally experience long delays or get error messages submitting messages to the Messaging Server MTA and/or report errors such as:
451 4.0.0 temporary error returned by alias expansion:
In some cases this can happen with amazing regularity. In one case an automated message was being sent once per minute and every 10 minutes those messages would be delayed for 10 minutes. For 9 minutes, messages would be processed and delivered instantly. For the next 10 minutes, none would be delivered, and then finally all the pending messages would be delivered again.
In other cases, this message will appear very sporadically for messages coming from internal addresses, and may also appear in "reprocess" logs occasionally.
By enabling slave debug on the channel on which the message arrives on the MTA, we found:
16:13:06.93: Remote host IDENT information: ...
16:13:06.93: Attempting channel switch: Rewriting "user@[...]"
16:13:06.93: Rewrite succeeded, matched channel tcp_intranet
16:13:06.93: Rewrite/switch succeeded, switched to channel: tcp_intranet
16:13:06.93: Received : "MAIL FROM:<> ...
16:13:06.93: Debug output enabled, system <local-MTA-hostname>, process <pid>.<thread>,...
16:21:16.48: Sending : "250 2.5.0 Address and options OK."
16:21:16.48: Received : "RCPT TO:<> ...
Notice the 8+ minute jump in the time stamps between when MAIL FROM was received and when the response was sent.
Doing pstack on the tcp_smtp_server process during that time showed the thread was waiting for response from the LDAP server - trying to look up the sender's domain:
ffffffff7b4d9de8 pollsys (1001aa260, 5, ffffffff75ee2070, 0)
ffffffff7b46eb5c poll (1001aa260, 5, 1b7740, 0, 0, 0) + 88
ffffffff7a51a3d4 nsldapi_iostatus_poll (100356150, ...) + dc
ffffffff7a521cfc wait4msg (100356150, 9, 1, 0, ...) + 7fc
ffffffff7a520f30 nsldapi_result_nolock (100356150, 9, 1, 1, ...) + 80
ffffffff7d81f698 dmap_loc_domain (ffffffff75ee3268, ...) + 848
ffffffff7ea001e0 smtpc_enqueue (0, ffffffff75ef26f0, ...) + 15b0
00000001000042f4 tcp_smtp_slave (100003e80, ...) + 224
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