[CentOS] Re: Postfix smtp freezing

[Jason Ross]

Rick,

The reason i used top was because I noticed that mailscanner and smtpd 
were always on the list UNLESS the issue was occurring.
I will try ps + grep next time as well.
As for the ips they resolve quickly however they are all listed in 
/etc/hosts as we do not have an internal DNS.

-jr

replies-lists-a1z2-centos at listmail.innovate.net wrote:
> using "top" to look for processes probably isn't the best approach as
> (by default) you'll only see the more resource intensive applications.
> you'll probably get a better picture of things related to a specific
> application using "ps" (and grep).
>
> when you connect to an MTA (e.g., postfix/sendmail) it will try to do
> an reverse map lookup on the ipnumber of the inbound connection. if you
> don't have in-addr.apra entries for your ipnumbers, or if the machine
> running your MTA is having trouble getting to the dns server for the
> ipnumber range, then you'll get the type of delays you seem to be
> seeing. ultimately the dns will time out (the number of dns servers you
> have listed in your mail server's /etc/resolv.conf will effect this -
> more is not better).
>
> you can get a sense of whether this is the issue by doing lookups (on
> the mail server) of the ipnumber(s) for connecting machines that are
> encountering the delay. depending on your configuration, your server
> may  cache a result, so the first may be slow with subsequent ones
> being fast (until you hit the TTL on the record).
>
> [by the way, when sending to a mailing list please try to suppress your
> confidentiality notice as it's meaningless in this context, and takes
> up a lot of lines.]
>
>   - Rick
>
>