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Slow SMTP connection when using IPv6

Setup:

OS X 10.4.11 Server configured to supply mail services.
Server is behind IPv4 firewall and NAT box.
IPv4 ports 25, 465, and 587 forwarded to server.
Server has automatic IPv6 address and router tunnels IPv6 connections.
Ports are open for 25, 465, and 587 for IPv6 connections.

When sending mail from hosts on the IPv4 network, connections to the SMTP server seem to proceed normally.
When sending mail from hosts via IPv6 network, connections take a long time to be established or time out.

Any ideas would be appreciated.

iMac, Mac OS X (10.3.x)

Posted on Feb 18, 2009 10:40 PM

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Posted on Feb 20, 2009 5:56 PM

Okay, after some further work, I found the issue. I turns out it was not related to the IP version that I used, but another change in the firewall settings. Stealthing TCP and UDP ports was the cause of the delay in connection. Once stealth mode was turned off, SMTP connections proceeded at a normal pace.
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Slow SMTP connection when using IPv6

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