Sender verify callout option not rfc compliant.

[4u123]

Many mail servers deliberately stall the display of the SMTP greeting by 30s or more. Any compliant mail system will wait until the greeting banner is displayed. The RFC standard says that the connecting server should wait up to 300 seconds.

When the cpanel server is trying to perform the sender verify callout and the greeting is stalled by 30s or more, it's at this point that the cpanel server reaches timeout. The cpanel server incorrectly assumes that the server it is connecting to isnt listening, when in actual fact, it is going through the stall period.

Is there anything in the exim configuration that can be changed to make this work ?

[webignition]

Callout verification can be specified with a range of optional parameters, some of which relate to timeouts.

http://exim.org/exim-html-4.50/doc/h...39.html#IX2589
http://exim.org/exim-html-4.62/doc/h...CALLaddparcall

The first link is the spec relating to the version of Exim you're probably running. The second, for Exim 4.6.x, covers the same points but, at least for me, did so in a more understandable manner.

Changing:

require verify = sender/callout

to:

require verify = sender/callout=300s

should result in setting a 300s (5 minute) timeout for the whole callout process.

Other timeouts for specific parts of the callout (such as the timeout for establishing an SMTP connection) can also be specified, as explained in the docs.

[4u123]

Very nice, thank you

[rpmws]

this is a very interesting thread I have a question ..what would be the drawback if any to setting this parameter higher like this?